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GUIDE FOR THE OPERATIONAL USE 
GU
OF ID
 SPE F
E OR
D  T
 ANHDE OP
 REDE-R
LIATI
GHON
T A
 OFL U
FE S
N E
C  E 
OF SPE
D ED A
TEC N
TID R
ONE D-
TE L
C IGH
HN T
O  OF
L F
OG E
Y NCE 
DETECTION TECHNOLOGY
VERSION NUMBER: 
Version 1.2
VER
DA SION NUMBER:
TE: 
 
Version 1.3
December 2015
DATE: 
October 2015
Copyright © 2015. All rights reserved. Association of Chief Police Officers of England, Wales and Northern Ireland.
Regis
Cop tered number: 344583: 25 Vict
yright © 2015. All rights reserv oria Str
ed. Na eet, London. S
tional Police ChieW1H 0EX
fs’ Council.

GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
AMENDMEN T S
Version 1.2 dated December 2015 contains amendments within the following chapters:
Chapter 1: 
Home Office Type Approval
Chapter 4: 
Equipment Classification
Chapter 6: 
Speed Detection Using a Speedometer Fitted to a Patrol Vehicle
Chapter 8: 
Radar Speedmeters (across the road)
Chapter 10:    Laser Speedmeters
 
Additional chapter:
Chapter 17:    Red-light Enforcement Cameras
Please note:
In April 2015 the National Police Chiefs’ Council (NPCC) replaced the Association of Chief 
Police Officers’ (ACPO). This document makes some historic references, where applicable, 
to ACPO and ACPO approval.
© NPCC 2015 Version 1.2


GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
FO RE WO RD
Efforts  of  road  safety  partnerships  and  police  forces  across  the  country  are 
continuing in an attempt to reduce the number of people kil ed or seriously injured 
on our road network.
The UK has some of the safest roads in the world and countries around the globe are 
adopting our approaches to road safety. This success is achieved by using a number 
of  initiatives  including  preventative  road  safety  activity,  enforcement  of  traffic 
laws  and  driver  education  schemes.  Roads  policing  enforcement  technology  has 
developed greatly in recent times and continues to play a crucial role in encouraging 
motorists to respect traffic laws and in bringing offending drivers to justice.
This guidance is provided to ensure we continue to improve safety on our roads and 
maintain public confidence in the integrity of the technology being used to identify 
offending motorists.
Before equipment can be used to provide evidence that can be made admissible in 
court, Home Office Type Approval (HOTA) of this technology is required. Equipment 
is thoroughly tested and is not submitted for approval until scientists are satisfied 
with the integrity of the technology. HOTA provides an assurance of the technical 
accuracy and reliability of all approved devices.
This document, produced by the National Police Chiefs’ Council (NPCC), provides 
guidance  for  those  using  enforcement  technologies  on  how  Type  Approved 
equipment  should  be  operated  and  an  understanding  of  what  may  affect  its 
performance. It also provides an understanding of the reasons behind the advice 
in the manufacturers’ instruction manuals, as well as practical advice to improve 
operational use.
Maintaining  public  confidence  in  enforcement  technology  is  key  to  ensuring  the 
public’s continued trust in the technologies used in helping reduce offending on our 
roads and making them safer.
Steve Barry
Assistant Chief Constable, Sussex Police
NPCC lead, Roads Policing Enforcement Technology
© NPCC 2015 Version 1.2
1

GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
CONTENTS
Introduction  ................................................................................................................................6

Home Office Type Approval  ........................................................................ 8
1.1 
What is Home Office Type Approval (HOTA)?  ........................................................8
1.2 
Roads Policing Enforcement Technology (RPET) group  ..........................................8
1.2.1  
RPET group terms of reference ...............................................................................9
1.3 
Where can information on HOTA be found?  ..........................................................10
1.4 
What is the HOTA process?  ....................................................................................10
1.5 
Does the RPET group act as a consultancy or provide design advice?  ...................11
1.6 
What is the advantage of HOTA?  ............................................................................11
1.7 
ACPO approved devices  .........................................................................................11
1.8 
Non-approved equipment ......................................................................................12
1.9 
What could invalidate HOTA?  .................................................................................12
1.10  
Can HOTA devices be altered at all?  .......................................................................13
1.11  
Who is responsible for maintaining HOTA standards?  ...........................................13

Health and Safety Act  ................................................................................. 14
2.1 
Roadside enforcement precautions  .......................................................................14

Operational Training  ................................................................................... 15
3.1 
Objectives for training enforcement device operators ...........................................15
3.2 
Additional training objectives for time/distance devices ........................................15

Equipment Classification  ............................................................................ 16
4.1 
Attended actively operated  ....................................................................................16
4.2 
Automatic operation ...............................................................................................16
4.3 
Unattended automatic operation ...........................................................................17
4.4 
Supervised automatic operation  ............................................................................17

Cosine Effect  ...............................................................................................18
5.1 
What is it?  ..............................................................................................................18
5.1.1  
Rule of thumb .........................................................................................................18
5.2 
How does it work?  .................................................................................................19
5.3 
Good practice ..........................................................................................................21
5.3.1  
Hand-held and portable speedmeters  ...................................................................21
5.3.2  
Fixed cameras/speedmeters ...................................................................................22
5.4 
Additional considerations  ......................................................................................22

Speed Detection Using a Speedometer Fitted to a Patrol Vehicle  ................ 23
6.1 
Means of check  ......................................................................................................23
6.2 
Minimum distance  .................................................................................................23
6.3 
Speedometer accuracy  ...........................................................................................23
2
© NPCC 2015 Version 1.2

GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY

Radar Speedmeters (hand-held)  ................................................................. 24
7.1 
Radar speedmeter technology description  ............................................................24
7.2 
Confidence checks ..................................................................................................25
7.2.1    
Sight alignment .......................................................................................................25
7.2.2    
Speed accuracy .......................................................................................................25
7.3 
Typical use  ..............................................................................................................25
7.4 
Precautions .............................................................................................................25
7.4.1    
General  ...................................................................................................................25
7.4.2   
Health and safety ....................................................................................................26
7.4.3    
Evidence  .................................................................................................................26

Radar Speedmeters (across the road)  ......................................................... 27
8.1 
Technology description  ..........................................................................................27
8.2 
Confidence checks ..................................................................................................27
8.2.1  
Alignment  ...............................................................................................................27
8.2.2  
Distance and speed accuracy ..................................................................................27
8.3 
Typical use ...............................................................................................................27
8.4 
Precautions .............................................................................................................28
8.4.1   
General....................................................................................................................28
8.4.2   
Health and safety  ...................................................................................................28
8.4.3   
Evidence ..................................................................................................................28

Parabolic Radar  .......................................................................................... 29
9.1 
Technology description  ..........................................................................................29
9.2 
Confidence checks ..................................................................................................29
9.2.1   
Alignment  ...............................................................................................................29
9.2.2   
Distance and speed accuracy ..................................................................................29
9.3 
Typical use  ..............................................................................................................29
9.4 
Precautions .............................................................................................................29
9.4.1   
General  ...................................................................................................................29
9.4.2   
Health and safety  ...................................................................................................29
9.4.3   
Evidence ..................................................................................................................29
10 
Laser Speedmeters  ..................................................................................... 30
10.1     
Laser speedmeter technology description  .............................................................30
10.2    
Confidence checks ..................................................................................................30
10.2.1 
Sight alignment .......................................................................................................30
10.2.2  
Distance and speed accuracy ..................................................................................31
10.3    
Typical use  ..............................................................................................................31
10.4    
Precautions .............................................................................................................31
10.4.1  
General  ...................................................................................................................31
10.4.2  
Health and safety  ...................................................................................................31
10.4.3  
Evidence  .................................................................................................................32
10.5   
Laser speedmeter check range  ..............................................................................32
10.5.1  
Description ..............................................................................................................32
10.5.2  
Range set-up ...........................................................................................................32
© NPCC 2015 Version 1.2
3

GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
CONTENTS
11 
Siting Considerations for Automatic Unattended Speedmeters .................... 33
11.1 
Site surveys ............................................................................................................. 33
11.2 
Unattended site set up ............................................................................................ 33
12 
In-car Distance/Time Devices  ..................................................................... 34
12.1 
Technology description ........................................................................................... 34
12.2 
Confidence checks .................................................................................................. 34
12.2.1  
Sight alignment ....................................................................................................... 34
12.2.2  
Distance and speed accuracy .................................................................................. 34
12.3 
Typical use ............................................................................................................... 35
12.3.1  
Overview  ................................................................................................................ 35
12.3.2 
Follow check ........................................................................................................... 35
12.3.3  
Pre-fed distance check ............................................................................................ 36
12.3.4  
Being followed ........................................................................................................ 36
12.3.5  
Crossing check ......................................................................................................... 36
12.3.6  
Dial in distance check .............................................................................................. 36
12.4 
Precautions ............................................................................................................. 37
12.4.1  
General  ................................................................................................................... 37
12.4.2  
Health and safety  ................................................................................................... 37
12.4.3  
Evidence  ................................................................................................................. 37
13 
Automatic Distance/Time Devices  .............................................................. 38
13.1 
Technology description ........................................................................................... 38
13.2 
Confidence checks .................................................................................................. 38
13.2.1  
Site alignment  ........................................................................................................ 38
13.2.2  
Distance and speed accuracy .................................................................................. 38
13.3 
Typical use ............................................................................................................... 39
13.4 
Precautions ............................................................................................................. 39
13.4.1  
General  ................................................................................................................... 39
13.4.2  
Health and safety  ................................................................................................... 39
13.4.3 Evidence 
 ................................................................................................................. 39
14 
Chronometers  ............................................................................................ 40
14.1 
Technology description ........................................................................................... 40
14.2 
Confidence checks .................................................................................................. 40
14.2.1  
Sight alignment ....................................................................................................... 40
14.2.2  
Timing check  .......................................................................................................... 40
14.2.3  
Distance and speed accuracy .................................................................................. 41
14.3 
Typical use  .............................................................................................................. 41
14.4 
Precautions ............................................................................................................. 41
14.4.1   
General  ................................................................................................................... 41
14.4.2  
Health and safety .................................................................................................... 41
14.4.3  
Evidence  ................................................................................................................. 41
4
© NPCC 2015 Version 1.2

GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
CONTENTS
11 
Siting Considerations for Automatic Unattended Speedmeters .................... 33
15 
Sensor Operated Roadside Speedmeters  .................................................... 42
11.1 
Site surveys ............................................................................................................. 33
15.1 
Technology description ........................................................................................... 42
11.2 
Unattended site set up ............................................................................................ 33
15.2 
Confidence checks .................................................................................................. 42
12 
In-car Distance/Time Devices  ..................................................................... 34
15.2.1  
Alignment  ............................................................................................................... 42
12.1 
Technology description ........................................................................................... 34
15.2.2 
Distance and speed accuracy  ................................................................................. 42
12.2 
Confidence checks .................................................................................................. 34
15.3 
Typical use ............................................................................................................... 42
12.2.1  
Sight alignment ....................................................................................................... 34
15.4 
Precautions  ............................................................................................................ 43
12.2.2  
Distance and speed accuracy .................................................................................. 34
15.4.1  
General  ................................................................................................................... 43
12.3 
Typical use ............................................................................................................... 35
15.4.2  
Health and safety .................................................................................................... 43
12.3.1  
Overview  ................................................................................................................ 35
15.4.3  
Evidence .................................................................................................................. 43
12.3.2 
Follow check ........................................................................................................... 35
16 
Cameras ...................................................................................................... 44
12.3.3  
Pre-fed distance check ............................................................................................ 36
16.1 
Technology description  .......................................................................................... 44
12.3.4  
Being followed ........................................................................................................ 36
16.2 
Confidence checks .................................................................................................. 44
12.3.5  
Crossing check ......................................................................................................... 36
16.2.1  
Site alignment ......................................................................................................... 44
12.3.6  
Dial in distance check .............................................................................................. 36
16.2.2  
Distance and speed accuracy  ................................................................................. 45
12.4 
Precautions ............................................................................................................. 37
16.2.3  
Evidence .................................................................................................................. 45
12.4.1  
General  ................................................................................................................... 37
17 
Red-light Enforcement Cameras  ................................................................. 46
12.4.2  
Health and safety  ................................................................................................... 37
17.1 
Technology description  .......................................................................................... 46
12.4.3  
Evidence  ................................................................................................................. 37
17.2 
Confidence checks .................................................................................................. 47
13 
Automatic Distance/Time Devices  .............................................................. 38
17.2.1   
Red-light in offence image ...................................................................................... 47
13.1 
Technology description ........................................................................................... 38
17.3 
Typical use ............................................................................................................... 47
13.2 
Confidence checks .................................................................................................. 38
17.4 
Precautions  ............................................................................................................ 47
13.2.1  
Site alignment  ........................................................................................................ 38
17.4.1  
General  ............................................................................................................. 47
13.2.2  
Distance and speed accuracy .................................................................................. 38
17.4.2  
Health and safety .............................................................................................. 47
13.3 
Typical use ............................................................................................................... 39
17.4.3  
Evidence ............................................................................................................ 47
13.4 
Precautions ............................................................................................................. 39
13.4.1  
General  ................................................................................................................... 39
13.4.2  
Health and safety  ................................................................................................... 39
13.4.3 Evidence 
 ................................................................................................................. 39
14 
Chronometers  ............................................................................................ 40
14.1 
Technology description ........................................................................................... 40
14.2 
Confidence checks .................................................................................................. 40
14.2.1  
Sight alignment ....................................................................................................... 40
14.2.2  
Timing check  .......................................................................................................... 40
14.2.3  
Distance and speed accuracy .................................................................................. 41
14.3 
Typical use  .............................................................................................................. 41
14.4 
Precautions ............................................................................................................. 41
14.4.1   
General  ................................................................................................................... 41
14.4.2  
Health and safety .................................................................................................... 41
14.4.3  
Evidence  ................................................................................................................. 41
© NPCC 2015 Version 1.2
5

GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
INTRODUCTION
The  Road  Traffic  Offenders’  Act  1988  (amended  by  the  Road  Traffic  Act  1991)  allows  for  the  Type 
Approval of devices to be used for the detection of the speed of motor vehicles. The Home Office’s 
Centre for Applied Science and Technology (CAST) and National Police Chiefs’ Council (NPCC) Roads 
Policing Enforcement Technology (RPET) group specify and operate the Type Approval process to assure 
that equipment that attains the award of Type Approval is of the required accuracy and is resistant to 
error. Testing is challenging and rigorous, making the UK Type Approval one of the most exacting and 
sought after certifications of police enforcement equipment available worldwide. 
The  evidence  from  Type  Approved  equipment  is  therefore  of  high  integrity and  inherently  reliable. 
The purpose of this guide is to allow operators of Type Approved equipment to achieve a consistent 
standard wherever it is used to support prosecutions for speed and red-light offences.
Calibration of equipment is not a condition of Type Approval within the meaning of the Road Traffic 
Offenders’ Act Section 20(4) and, therefore, failure to prove calibration does not affect the admissibility 
of evidence. While it is not a condition, it is recommended that calibration is performed on an annual 
basis as normal routine maintenance of the device.
The speed of traffic is a significant factor in the severity of injury in road traffic collisions. Government 
and industry research has shown that the use of excess and excessive speed is common, making the 
requirement  for  speed  management  a  necessary  measure  in  the  reduction  of  the  volume  of  road 
traffic-related  injuries.  While  education  and  engineering  are  important  in  the  treatment  of  traffic 
system casualty rates, enforcement of speed limits remains an important and immediate requirement 
in support of those measures for the foreseeable future.
This guide provides advice on operating practices to maintain a consistent speed enforcement facility 
to drive down casualties and provide public confidence in police-led road traffic enforcement.
The devices referred to in this guide are subject to rigorous field and laboratory testing to ensure the 
accuracy and reliability of their measurements and to prevent the possibility of spurious measurements 
being produced. Manufacturers’ instructions should be followed to ensure results meet Home Office 
Type Approval and those proven during testing.
Manufacturers’ instructions are assessed along with the equipment during the Type Approval process. 
They are later changed only with the permission of CAST, after an amendment request is received 
along with the amended manual. The manufacturers’ instructions therefore form the most relevant 
operating procedures to be carried out when operating each piece of equipment. This guide explains 
the reasoning behind some of the instructions in operator manuals but is subservient to them.
6
© NPCC 2015 Version 1.2

GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
The advice in this guide should be used to enhance the operators’ understanding of the principles used 
by the equipment and to avoid misuse, which has the potential to affect accurate speed measurement 
of target vehicles.
While the practice described in this manual assists users in the trouble-free operation of roads policing 
enforcement equipment, there is no legal requirement that the guide is followed; however, the practice 
contained herein will reduce the potential for mistakes in procedure.
NOTE:
Compliance   with   the   guidance   in   this   document   is   not   a   condition   of   Type   Approval.  
Non-compliance  with  the  suggested  practice  herein  by  a  police  officer,  partnership, or    rep-
resentative   of    a    partnership    does    not    mean    that    any    speed    measurement obtained 
is necessarily inaccurate.
© NPCC 2015 Version 1.2
7

GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY

HOME OFFCE TYPE APPROVAL
1.1 
What is Home Office Type Approval (HOTA)?
 
HOTA is a process that is designed to ensure devices are accurate, reliable and robust and 
provide accurate evidence leading to safe convictions.
 
HOTA is granted for enforcement devices that are intended for police use and have been 
manufactured or supplied to meet the strict criteria laid down in handbooks produced by 
CAST. If the device meets the criteria and is successful in Type Approval testing the supplier 
and the Home Office enter into a Type Approval agreement. This places a strict contractual 
obligation  on  the  supplier  to  ensure  all  devices  supplied  for  roads  policing  enforcement 
in England, Northern Ireland, Scotland and Wales comply exactly with the devices tested. 
Evidence from equipment that is awarded HOTA is admissible in court by way of certification 
of the record in accordance with Section 20 of the Road Traffic Offenders’ Act 1988, Speeding 
Offences etc: admissibility of certain evidence. Prescription Orders in the form of Statutory 
Instruments (SI) describe devices in a generic way. HOTA of individual makes and models 
fitting that description are then made by a Ministerial Approval for equipment that passes 
the CAST and RPET testing.
 
Day-to-day management of the HOTA process is provided by Road Safety Support (RSS).
1.2 
Roads Policing Enforcement Technology (RPET) group
 
RPET  has  a  nominated  chief  police  officer  who  is  a  member  of  the  NPCC  Roads  Policing 
Business Area. The NPCC lead meets with the Home Office Road Crime Section at a strategic 
level  to  address  RPET  operational  and  Type  Approval  challenges.  The  NPCC  lead  neither 
recommends nor makes decisions on Type Approval; this is a Home Office responsibility. The 
secretariat to the NPCC lead is provided by RSS. 
 
RPET also operates a user forum, chaired by RSS, which addresses issues affecting the use, 
testing and development of roads policing technology. 
 
The forum has no decision-making power, and any issues raised through the group will be 
brought to the attention of the NPCC lead through the chair of the group.
 
Delegates for the user forum are drawn from:
 
1  Roads policing officers/road safety partnership staff
 
2  Home Office
 
3 CAST
 
4  Crown Prosecution Service (CPS)
 
5  Industry and suppliers
 
Other persons can be co-opted onto the user forum to provide technical, legal or operational 
expertise.  The  user  forum  meets  regularly  to  progress  issues  arising  from  its  terms  of 
reference.
 
In between meetings RSS continues to progress issues relating to devices undergoing HOTA 
testing and provides a liaison between the operational officer, manufacturers, Government 
agencies and NPCC.
8
© NPCC 2015 Version 1.2

GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
 
The first point of contact for any query relating to roads policing enforcement equipment should 
be the secretariat to the NPCC lead for RPET, RSS at: RPET Secretariat, Road Safety Support, 
PO Box 10092, Billericay, Essex, CM12 9UY or email: xxxxxxxxxxxx@xxxxxxxxxxxxxxxxx.xx.xx
1.2.1  
RPET group terms of reference
 
Secretariat - provided through RSS:
•   The secretariat support to the NPCC lead for RPET will manage the day-to-day business of 
the user forum
•   Provide a full secretariat from staff suitably qualified to deal with technical testing and legal 
problems
•   Interface with the enforcement technology industry and manage all approvals through the
  HOTA process
•   Supervise and arrange all police operational testing
•   Work with the Home Office Road Crime Section and CAST to deliver fully tested reliable 
devices to recommend to full HOTA
•   Ensure  the  NPCC  lead  for  RPET  chair  is  fully  briefed  on  any  potential  issues  relating  to 
technology or legal challenges to technology or HOTA
•   Maintain  the  NPCC  Guide  for  The  Operational  Use  Of  Speed  And  Red-Light  Offence 
Detection Technology
•   Represent RPET at all events and with industry
•   Provide an expert prosecution witness in cases where expert defences are raised in relation 
to the HOTA of a device 
•   To  examine,  review  and  make  recommendations  on  technical  aids  for  roads  policing 
enforcement technology to the police service
•   To examine and introduce new technology for casualty reduction
•   To consider and report on any roads policing enforcement technology matter referred to 
the Home Office Roads Crime Section Type Approval Strategic Group
 
The RPET group:
•   To  examine,  review  and  make  recommendations  on  technical  aids  for  roads  policing 
enforcement technology to NPCC and, where HOTA is to be granted, to the Home Office 
based on advice from CAST and the RPET secretary
•   To examine and introduce new technology for casualty reduction
•   To consider and report on any roads policing enforcement technology matter referred to 
the group
•   A sub group called the Safety Camera Administration Group is managed by the RPET sec-
retary. It provides policy advice on the use of speed and red-light enforcement equipment. 
All  guidance  produced  is  submitted  and  approved  through  the  RPET  group  before  it  is  
issued
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HOME OFFICE TYPE APPROVAL
 
For England and Wales
•   To consider legal issues arising from the use of technology
•   To consider legal issues around the use of existing and new technologies
1.3 
Where can information on HOTA be found?
 
Any person or organisation can obtain a copy of a statutory instrument from HM Stationery 
Office, or copies of orders issued from January 1998 onwards can be obtained from the Home 
Office.
1.4 
What is the HOTA process?
 
The  process  for  acquiring  Home  Office  Type  Approval  has  two  parts:  a  Roads  Policing 
Enforcement Technology part followed by a Home Office part.
 
RSS coordinates the process as well as making assessments of the equipment’s suitability to 
meet the operational needs of the UK police forces. When the equipment is accepted into 
the process and after CAST has made its technical assessments, RSS arranges with a number 
of police forces to test mobile and fixed devices under operational conditions. This includes 
assessing whether the equipment is easy and simple to use and produces consistently 
accurate readings without special skills. A device that produces a mixture of accurate and 
inaccurate readings in normal use will fail the Type Approval testing. A device that produces 
a mixture of accurate and no readings will pass unless the quantity of “no readings” suggests 
it is too difficult and therefore impractical for use by operational officers.
 
CAST makes a detailed technical assessment of devices, as well as technical and operational 
documentation,  to  ensure  they  are  compliant  with  the  requirements  of  the  speedmeter 
handbook relevant for the prescribed sort of equipment. They also submit the equipment to 
one of a number of approved independent test houses for functional testing of the equipment 
to ensure it meets the required specifications in the speedmeter handbook.
 
If  the  equipment  has  met  the  requirements  by  passing  the  assessment  and  testing  by 
CAST,  the  police  forces  and  an  independent  test  house,  a  recommendation  from  CAST  is 
given to the Home Office Minister for the issue of a Type Approval Agreement. The Type 
Approval Agreement is a contract between the Home Office and the supplying company to 
set out the terms which each must observe. Breach of a term of the agreement by a supplier 
could potentially lead to suspension or revocation of the approval. Once the Type Approval 
Agreement is signed, the Type Approval is signed by the Home Office Minister.
The details of the HOTA process are laid down by CAST.
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1.5 
Does the RPET group act as a consultancy or provide design advice?
 
The strict answer is no, but realistically one must accept that suppliers may glean some guidance 
through RSS, the secretariat support, from the discussions around their demonstrations.
 
However, the RPET secretary works within ‘commercial in confidence’ terms. This means that 
no member may openly discuss any aspect of any device or component (including software) 
not already placed in the public domain by the commercial concern.
 
Thus, the RPET secretary cannot, and will not give advice to a commercial concern in respect 
of research and development issues. They will comment on the operational acceptability of 
devices under demonstration or test, but market research and product placement are wholly 
issues for the commercial concern.
 
The adherence to ‘commercial in confidence’ also means members cannot advise any person 
or organisation of the suitability or performance of devices which are, or have been, within 
the HOTA process.
1.6 
What is the advantage of HOTA?
 
Section 20 of Road Traffic Offenders’ Act 1988 allows for the evidence from Type Approved 
and prescribed devices to be admissible in court by way of certification. The approval process 
gives the public and the courts reassurance that measurements from a particular device can 
be relied upon as evidence.
1.7 
ACPO approved devices
 
Some devices do not have HOTA; instead, these time/distance devices are ACPO approved. 
The main reason for this is their extreme level of operator interaction and attention during 
operation.
 
The devices themselves can perform calculations with 100% accuracy but the speed will only 
be as accurate as the data from which it did the calculation; i.e. the skill of the operator 
in pressing switches at exactly the right time. The police officer has to enter the time and 
distance travelled and is often in a position to correlate the derived speed with that shown 
on the police vehicle speedometer.
 
With these devices, the more likely legal challenge is to the accuracy of the operator rather 
than that of the device, but without the protection of Type Approval its operator will need to 
be able to explain in basic nontechnical terms how the device works.
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HOME OFFICE TYPE APPROVAL
 
ACPO no longer approves roads policing enforcement technology. Any approval granted by 
ACPO ceased to be effective after December 2012. After that date these devices no longer 
have ACPO approval.
1.8 
Non-approved equipment
 
As far as the law is concerned, the only stipulation is that one person’s opinion of a vehicle’s 
excessive speed is insufficient without corroboration (Section 89(2) Road Traffic Regulation 
Act  1984),  with  the  exception  of  motorways  where  only  one  witness  is  required.  That 
corroboration can be from another witness who is of the same opinion or from any electrical 
or mechanical device where accuracy and reliability can be established.
 
There is no requirement in law for corroboration to come from a HOTA or ACPO approved 
device or only from devices being used strictly in accordance with their handbook or this 
guide. A pre-measured distance plus a witness with a stopwatch is still legally valid.
 
The  difference  that  HOTA  makes  is  that  the  court  will  assume  the  device  is  reliable  and 
accurate and allow its ‘record’, if any, to be entered by way of a certificate. For all other 
devices a witness will have to satisfy the court of the equipment’s reliability and accuracy.
1.9 
What could invalidate HOTA?
 
Once  HOTA  is  granted  unauthorised  changes  should  not  be  made  to  the  device  by  the 
manufacturers, manufacturers’ agents or operators.
 
Examples include a change or addition to:
•   The device hardware or software
•   Any enclosure constructed to house the device during operational use
•   An unauthorised connection to an unapproved power source
•  The method of secondary check
 
This means devices should only be used with agreed power sources, enclosures, software 
and approved leads or connections. They can only be used within the enclosures approved 
for that specific device. Nothing should be placed in an enclosure that is not included within 
Type Approval when the device is being used for enforcement purposes. If these rules are 
not  followed  a  court  may  decide  that  it  is  no  longer  the  Type  Approved  device,  thereby 
removing the presumption it is reliable and accurate and potentially rendering its evidence 
inadmissible (Breckon v DPP [2007] EWHC 2013 (Admin)).
 
Changes to devices may be made by manufacturers and manufacturers’ agents on application 
to and approval by CAST.
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1.10   
Can HOTA devices be altered at all?
 
HOTA devices can be altered but only after strict agreement with CAST and The Home Office. 
At any time the supplier may apply to CAST to make additions or amendments to the device, 
its software or any other component parts, or to the operators’ manual. The supplier cannot 
make  the  change  without  prior  written  agreement.  Some  minor  changes  may  be  agreed 
on the supply of technical specifications and explanations to CAST but other changes may 
require full or partial re-testing. CAST will specify the tests required.
1.11   
Who is responsible for maintaining HOTA standards?
 
The  Home  Office,  NPCC  lead  for  RPET,  the  equipment  suppliers  and  the  operators  share 
responsibility for ensuring devices remain within the specification agreed for the HOTA.
 
For the Home Office, NPCC lead for RPET and the operator it is a matter of the integrity of the 
process; for the supplier it is a contractual obligation. The Home Office reserves the right to 
suspend or revoke Type Approval.
 
The operator should check to ensure a device is calibrated annually. Annual calibrations can 
only be carried out by the manufacturer or organisations approved by CAST. Devices used for 
speed enforcement which are not mechanical and, therefore do not wear, do not have to be 
regularly adjusted to maintain accuracy. Annual calibration is not a condition of HOTA but it 
is good practice to use equipment that has a calibration that is in date.
 
Type  Approved  devices  will  have  a  sticker  applied  to  them  showing  the  date  of  the  last 
calibration and the due date of the next calibration. It is acceptable for devices to display the 
date of the next calibration on their data screen in lieu of a sticker.
 
The annual calibration should not be confused with the periodic confidence checks of devices 
against known distances or speeds. These periodic checks are an optional or required part of 
the operators’ procedures and are detailed in the operators’ handbooks for the equipment.
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HEALTH AND SAFETY ACT
 
Roads policing enforcement must be carried out in compliance with legislation and guidance.
 
All devices referred to within this guide have been tested and conform to current safety 
parameters.  Operators  and  road  users  may  be  exposed  to  unnecessary  danger  when 
technology is used inappropriately or outside guidelines.
 
All personnel must remain aware of the hazardous nature of such policing activity and the 
constant need for safe working practices.
 
Risk assessments must be completed for all enforcement activity and where the advent of 
new technology or changes in the working environment dictates such a need.
 
Specific  instructions  or  health  and  safety  precautions  for  individual  technologies  and 
equipment types are shown within the “Precautions/Health and Safety” sections of each 
technology element of this manual.
2.1    
Roadside enforcement precautions
 
When  carrying  out  roadside  enforcement  activity  that  has  the  potential  to  bring  the 
enforcement officer to conflict or contact with traffic the following should be observed:
1  High  visibility  clothing  manufactured  to  a  recognised  standard  should  be  worn.  The 
British Standard and European Standard for high visibility warning clothing is BS EN 471
2  In speed limits up to and including 40mph a visibility of a minimum of 60 metres should 
be maintained
3  In speed limits above 40mph a visibility of a minimum of 100 metres should be maintained. 
The guidance above is intended to allow oncoming motorists to avoid collision with 
enforcement personnel. Failure to follow it will not render the evidence of the officer 
inadmissible or provide any defence
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OPERATIONAL TRAINING 
 
All training should be documented and a robust audit trail maintained to assist in the rebuttal 
of any challenge to the competency of operators.
3.1    
Objectives for training enforcement device operators
 
NPCC recommendations are that the duration of training should be sufficient to enable an 
operator to qualify for the award of Certificate of Competence.
 
At the conclusion of the course the student will:
1  Understand the basic principles of roads policing enforcement technology as outlined in 
this document and manufacturers’ instructions
2  Demonstrate  their  ability  to  safely  carry  out  checking,  accuracy  tests  and  operating 
techniques applicable to devices used
3  Be competent in the presentation of evidence
3.2    
Additional training objectives for time/distance devices
 
It is recommended that all training be carried out using similarly equipped vehicles with car-
to-car communications.
 
At the conclusion of the course students will:
1  Demonstrate an understanding of the principles and safe operation of the in-car speed 
detection device(s)
2  Be able to calibrate the device(s) when required
3  Be able to carry out calibration checks
 
A  trained  police  operator  must  be  aware  of  the  basic  technical  functions  of  the  device. 
However, it is not necessary for them to be technically qualified to give evidence on principles 
of  the  system  nor  the  internal  workings  of  the  device.  If  such  evidence  is  required,  then 
the Crown Prosecution Service (CPS) in England and Wales, the COFPS in Scotland and PPS 
in Northern Ireland should ensure an expert witness is called liaising with the RPET group 
secretariat to provide an expert.
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EQUIPMENT CLASSIFICATION
 
Roads policing enforcement equipment use is classified in groups according to the operating 
method of each device. Some equipment is Type Approved for use in more than one operating 
method. The groups are described as follows:
4.1 
Attended actively operated
 
Equipment designed to be set up and actively operated by a trained user. The accuracy of 
the evidence from such equipment is verified by the operator in every case at the time of 
the offence. Such equipment may or may not record an image of an offending vehicle, but its 
operations are at all times supervised by the operator, whose own evidence of the offence is 
crucial.
 
Examples:
1  Hand-held laser
2  Hand-held radar
3  Mobile automatic radar
 
For all attended actively operated devices, the primary evidence is the measurement and 
record, if any, made by the device. The function of the operator is to be the human secondary 
check to verify that the speed recorded is consistent with what was seen at the time.
 
For  3,  the  function  of  the  operator  is  to  visually  confirm  that  what  appears  to  have 
automatically triggered the device was indeed travelling above the pre-set threshold, and at 
roughly the speed indicated, thereby providing a secondary check in locations with no marks 
on the road surface. The operator then resets the device to allow its continuous operation or 
notes any apparent discrepancies.
 
Operators should record evidence concerning the target vehicle, such as speed, direction of 
travel etc. Additionally, they should note any other significant factor that may have a bearing 
on the speed reading produced by the device. This may take the form of photographic or 
video records, or for basic hand-held operation may simply be a written note e.g. on a fixed 
penalty ticket.
4.2     
Automatic operation
 
A  speedmeter  which,  once  set  up,  works  by  itself  without  direct  and  continuing  human 
intervention and operates with an approved secondary check. Such equipment shall record 
an image of a speeding vehicle together with the time, date, speed and, if operated with a 
variable speed limit sign, direct evidence of the speed limit in force and displayed at that 
time.
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4.3    
Unattended automatic operation
 
Equipment  mounted  in  an  appropriate  housing  and  designed  to  operate  automatically. 
When the secondary check of speeds acquired with this type of equipment requires manual 
intervention to make a speed calculation to verify the primary speed, that check must be 
operated for each individual offence.
 
Examples:
1  Roadside loop operated speedmeter
2  Automatic average speed system
4.4 
Supervised automatic operation
 
Equipment designed to operate automatically but supervised to protect the equipment and 
the integrity of the evidence.
 
Examples:
1  Portable roadside radar speedmeter
2  Portable roadside laser speedmeter
3  Portable loop operated speedmeter
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COSINE EFFECT 
5.1    
What is it?
 
When a laser or radar speedmeter is used to detect the speed of a vehicle, the angle between 
the beam and the direction of travel of the vehicle will have the effect of reducing the speed 
that the speedmeter will sense from the target.
 
Since it is usually impractical to place the speedmeter directly into the path of the target 
vehicle, hand-held and fixed devices will be used from the side of or above the carriageway. 
There are occasions where devices may be directly in front of a target vehicle, such as on a 
bend; in these cases all of the target vehicle speed will be measured.
 
The angle of offset is controlled by how far the speedmeter is away from the path of the 
target vehicle, and the cosine of this angle approximates to the reduction in measured speed 
below the true speed.
 
Speedmeters are checked for accuracy so they show an accurate indication of the target 
vehicle; if the speedmeter is used at an angle that is large, i.e. the speedmeter is used at a 
distance that is a long way from the side of the road, the speedmeter cannot indicate a speed 
that is a good representation of the speed of the target vehicle. The accuracy of a reading 
from a target vehicle may therefore be compromised by its operating position.
 
To reduce this effect and make it easy to measure a good representation of target speed a 
“rule of thumb” method can be used.
5.1.1  
Rule of thumb
 
The distance to the target vehicle should be approximately 10 times the speedmeter offset 
from the centre line of the target vehicle path or above the road. 
 
This will reduce the effect to allow a minimum of 99.5% of the vehicle speed to be measured. 
Exceeding  the  suggested  offset  in  this  rule  of  thumb,  provided  the  device  is  kept  steady, 
simply creates a greater reduction in the measured speed as well as making a target more 
difficult to acquire.
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Note:
A  ratio  of  10  to  one  (10:1)  for  offset 
from  side  of  the  road  to  the  distance 
the vehicle is measured will mean that a 
minimum of 99.5% of the vehicle speed 
5.7°
will be sensed by the laser or radar 
speedmeter.
Cosine 5.7° = 0.995
100mph x 0995 = 99.5mph
100mph
100.5m
100m
99.5mph 
10m
Measurement Position
Figure 1 Practical il ustration of the “rule of thumb” for reducing Cosine Effect
5.2 
How does it work?
 
The laser speedmeter can only sense the distance travelled towards itself, not the distance 
being travelled along the road.
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COSINE EFFECT
0mph
0° 
15° 
Cosine 0° = 1
Cosine 15° = 0.966
100mph x 1 = 00mph
100mph x 0.966 = 6.6mph
100mph
100mph
96.6mph
Measurement Position
Figure 2 Cosine illustration one
The  left-hand  side  of  figure  2  shows  the  position  required  to  measure  the  true  speed  of 
a target vehicle. In practice the speedmeter will be used at the side of the road with the 
operator positioned in a lay-by, observation point or verge.
The right-hand side of figure 2 shows that the measurement point is now offset from the 
track of the vehicle. If the vehicle is still travelling at 100mph along its indicated track on 
the road and the speedmeter is operated from the side of the road creating an angle of 15° 
between the vehicle and the speedmeter, only a proportion of the vehicle’s speed will be 
measured.
The vehicle can be thought of as travelling at 100mph in the direction of its travel but at 
0mph at 90° to its travel or sideways; this is quite obvious. It is difficult, however, to make 
an assessment of the speed at an angle that is towards the speedmeter without resorting to 
some trigonometric calculations. The Cosine of 15°, in the example in the right-hand side of 
figure 2, can be used to calculate the speed towards the speedmeter position.
Further examples of this are shown in figure 3.
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GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
0mph
45° 
Cosine 45° = 0.707
100mph x 0.707 = 70.7mph
0mph
100mph
70.7mph
60°
Cosine 60° = 0.5
100mph x 0.5 = 50mph
Measurement Position
100mph
50mph
Figure 3 Cosine illustration two
 
Figure 3 shows that as the speedmeter is moved further and further away from the vehicle 
track  or  the  side  of  the  road,  the  angle  between  the  vehicle  track  and  the  speedmeter 
position increases; as the angle increases the speed sensed by the speedmeter decreases. If 
the speedmeter was at an angle of 90° pointing at the side of the vehicle, the speed sensed 
would be 0 mph.
5.3    
Good practice
5.3.1  
Hand-held and portable speedmeters
 
It is not practical for officers to make trigonometric calculations at every site so use the rule 
of thumb as described at 5.1.1 above.
 
If the speedmeter is too far from the carriageway the speed sensed by the speedmeter is 
reduced to a percentage that would mean that the speed reading is no longer representative 
of the speed of the target. If the rule of thumb is observed then the speed indicated will 
correspond to more than 99% of the speed of the target vehicle and is therefore representative 
of the true speed.
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COSINE EFFECT
5.3.2  
Fixed cameras/speedmeters
 
Fixed  devices  using  laser  or  radar  are  designed  to  work  at  a  fixed  angle  to  the  road  and 
usually have a fixed value set in their system to compensate for the angular offset to the road, 
and hence vehicle track. When the fixed system is installed the angle to the road and the 
fixed compensation will be set by the commissioning engineer for that installation. When the 
site is commissioned the supplier will check the site for accuracy. If desired, additional drive 
through tests to those performed by suppliers during commissioning may be undertaken by 
the police to confirm that the fixed installation is reading as expected.
 
Note: Unlike hand-held devices that do not have built-in compensation, it is possible for a 
fixed camera using compensation to over-read if the installation is not done correctly, so it is 
important that the system is checked after first commissioning.
5.4    
Additional considerations
 
In practice a speedmeter will be at an angle to the target vehicle in the horizontal and vertical 
planes and the effects of both will work in combination to reduce the speed sensed from the 
target vehicle by the speedmeter. The rule of thumb works for horizontal and vertical offsets. 
If a speedmeter is being used above and to the side of a vehicle track the reduction of the 
two offsets can be multiplied to approximate the effect of the speedmeter position.
 
For example:
 
99.5% (10m horizontal offset) x 99.5% (10m vertical offset) at a target range of 100 metres 
will result in approximately 99% of the target speed. This is an acceptable difference between 
the true and measured speed.
 
It should be noted that any effect will reduce the speed and differences in speed between 
that of the vehicle and that measured will always be to the advantage of the motorist.
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GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY

SPEED DETECTION USING A SPEEDOMETER FITTED 
TO A PATROL VEHICLE
 
This type of check, commonly known as the ‘follow check,’ has been used by police forces 
for a number of years and is readily accepted by the courts and motoring public alike. If the 
speedometer is used to support the suspicion of the officer then it is recommended that it is 
tested as detailed below.
6.1  
Means of check
 
It  is  preferred  that  a  roads  policing  vehicle  should  be  fitted  with  a  certified  calibrated 
speedometer that is regularly tested in accordance with force instructions. The use of non-
calibrated speedometers is not ideal but readings from them may still be acceptable in court, 
especially  if  the  margin  by  which  the  limit  is  exceeded  is  notable  and  the  non-calibrated 
speedometer would not be reasonably considered to be so inaccurate that the reading could 
not be relied upon.
 
The checking vehicle should be positioned to the rear of the suspected offending vehicle so 
as to maintain, throughout the check, an even distance between the vehicles.
 
Speedometer readings should be observed throughout and check start and end points related 
to readily identifiable features.
6.2   
Minimum distance
 
2/10 of a mile is the minimum distance recommended by NPCC for such a check.
6.3   
Speedometer accuracy
 
The patrol vehicle speedometer should be checked for accuracy at the end of a tour of duty 
after detection of an offending vehicle.
 
It is recommended that speedometer accuracy is checked using verifiable means.
 
It is recommended that the speedometer reading should be within ±2mph (plus or minus 
2mph) of the reading on the Type Approved device for calibrated speedometers. A record of 
the result should be made in an equipment log or a pocket notebook so the check result can 
be evidenced when required.
 
If a non-calibrated speedometer is used for a speed check the difference between it and the 
Type Approved device should be noted for later use in evidence of the assessed speed of the 
target vehicle.
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RADAR SPEEDMETERS (HAND-HELD)
7.1 
Radar speedmeter technology description
 
The  term  RADAR  is  an  acronym  for  Radio  Aid  to  Detection  And  Ranging;  a  radar 
transmitter sends electromagnetic radiation or radio waves from the device to the 
target vehicle and, provided the target vehicle is reflective to radio waves, these are 
reflected back to the radar receiver.
 
The frequency of the transmitted radio wave is known. A detector in the radar device 
can be made to compare the frequencies of the received and transmitted radio waves. 
If the frequency of the received radio wave is the same as that of the transmitted radio 
wave then the detector will show the speed of the reflecting target as being stationary. 
When the frequency of the received radio wave is higher or lower than that of the 
transmitted wave, the detector can be made to calculate a speed of the reflecting 
target. As the speed of the target increases the change in frequency becomes further 
from the original transmitted frequency. This works when a target is approaching or 
receding from the radar speedmeter.
 
The effect described above is known as the Doppler Effect.
 
Radar speedmeters use radio frequency emissions that are at a low power level so 
they will not interfere with the equipment in a target vehicle or other vehicles that 
come into the field of the radar.
 
Radar  speedmeters  will  typically  acquire,  quality  check,  calculate  and  display  the 
speed of a target vehicle in one to three seconds, with the operator being required to 
track and maintain a steady indicated speed for more than one measurement cycle of 
the radar speedmeter.
 
The  divergence  angle  of  the  beam  is  relatively  narrow  for  a  radar  beam;  typically 
between 12° to 20°. The beam width at the target increases as shown in the table 
below. Because the beam width is wider than the width of a typical vehicle at ranges 
as short as 50 metres, an operator should ensure that the vehicle being targeted is the 
vehicle in the beam of the radar speedmeter, and that is the vehicle causing the speed 
to be shown on the instrument.
Table 1 Beam width at typical target ranges
Target Range (m)
Beam Angle
100
200
300
400
500
15°
27
54
80
107
134
20°
36
73
109
146
182
 
The radar beam width in meters is shown in the shaded area of the table for beam 
angles of 15° and 20°.
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GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY
7.2 
Confidence checks
7.2.1  
Sight alignment
 
The  sighting  mechanisms  of  radar  speedmeters  are  rigid  and  are  generally  not 
adjustable; no alignment is required beyond that which is done by the manufacturer 
or supplier.
 
It may be useful to mark the approximate angle of the beam on the top of the radar 
speedmeter where possible to do so. This will give the operator a reasonable estimation 
of the approximate extent of the beam as the range to target increases.
7.2.2  
Speed accuracy
 
Radar speedmeters are not user adjustable and are not subject to wear that could 
cause a significant drift in speed accuracy. They may, however, be periodically tested 
for  speed  accuracy  with  the  aid  of  a  tuning  fork  that  will  vibrate  and  cause  a  pre-
determined speed to be read by the radar speedmeter when the tuning fork is held 
in the measuring radar beam. The tuning fork test will allow the instrument to be 
checked  to  confirm  that  no  changes  have  occurred  to  the  measuring  accuracy  of 
the instrument since its last calibration and servicing. The manufacturers’ handbook 
should be observed.
7.3 
Typical use
 
Radar speedmeters are typically used as hand-held devices; all of which are attended 
actively operated devices.
 
The speedmeter is aimed at the target vehicle at the front or rear with the radar beam 
being directed towards a target vehicle.
 
The vehicle will need to be tracked with the aiming sight to allow the instrument to 
make a satisfactory speed measurement of the target. Tracking of the vehicle should 
be  maintained  for  a  period  of  not  less  than  three  seconds.  At  the  same  time  the 
operator should consider whether the speed observed matches that indicated by the 
speedmeter. The speed can either be constant or show an accelerating or decelerating 
reading that is commensurate with the operator’s observations. When satisfied the 
reading is representative of the observations made the speed is locked into the device 
and recorded.
7.4 
Precautions
7.4.1  
General
 
Care should be taken to ensure that the radar speedmeter is used in a way that it only 
acquires reflections from the intended target vehicle. If there are two or more vehicles 
in the range of the radar then the strongest reflected signal will be the one that is used 
to indicate the speed to the operator.
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RADAR SPEEDMETERS (HAND-HELD)
  
Radar  speedmeters  can  be  used  by  operators  that  are  within  a  vehicle;  however,  the 
speedmeter must be at an open aperture and not be within the body of the vehicle to avoid 
reflections.
 
Sites for operation of radar speedmeters should be checked for possible sources of Radio 
Frequency  Interference  (RFI).  This  can  be  done  by  operating  the  radar  on  the  site  when 
there  are  no  vehicles  present  and  making  sweeps  through  180°  and  360°,  ensuring  the 
received signal strength is blank or the RFI indicator is not indicating unacceptable levels of 
interference.
 
Sites should also be checked to ensure that there are no radar reflective objects, such as 
metallic hoardings or signs that could cause unintended targets to be acquired by way of a 
reflected beam.
 
Sites  in  the  vicinity  of  obvious  radar  sources,  such  as  airports  or  military  establishments, 
should be avoided. Sites in the vicinity of mobile telephone masts do not present sources 
of RFI of sufficient strength to interfere with Type Approved radar speedmeters; it is good 
practice to avoid operating radar speedmeters within 50 metres of such masts even though 
adjacent operation would not present a source of error.
7.4.2  
Health and safety
 
Radar  devices  having  United  Kingdom  HOTA  comply  with  standards  that  are  designed  to 
ensure personal safety when operating the device. The maximum level of radiation when 
transmitting  is  below  the  UK  recommended  level  and  the  devices  can  be  considered 
absolutely safe for police use. No particular precautions are considered necessary. However, 
to avoid even low-level exposure it is recommended that the radar aerial should not be held 
closer than 25cms to the body.
7.4.3  
Evidence
 
The speed of the target vehicle should be noted on all occasions of a speed measurement.
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GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY

RADAR SPEEDMETERS (ACROSS THE ROAD)
8.1    
Technology description
 
Across the road speedmeters use the Doppler Effect to determine vehicle speed, however, 
unlike hand-held radar speedmeters (see the previous section) the across the road speedmeter 
has a fixed radar device that shines a radar beam across the road at a fixed angle. Because 
the angle to the road is known and, therefore the angle at which a target vehicle crosses that 
beam, a correction can be made in the speedmeter electronics to correct the Cosine Effect 
and record the vehicle speed.
 
Vehicle speeds are read directly from the speedmeter without further correction needing to 
be applied.
8.2    
Confidence checks
8.2.1  
Alignment
 
The fixed housing is aligned to the road and vehicle track at a site that is within limits of 
curvature that will have a minimum predicted effect on the measured speed of the vehicle 
after correction for Cosine Effect. The fixed housing is then equipped with a camera and radar, 
either permanently or on a scheduled basis. The fixed housing is constructed in a way that 
allows a camera technician to set the radar and camera in a fixed position that is aligned to 
the housing and hence the track of the vehicle.
 
Portable devices are aligned to the road by an alignment procedure at the start and end of 
the speed enforcement session.
8.2.2  
Distance and speed accuracy
 
Across the road speedmeters are checked at calibration and upon commissioning for speed 
accuracy and can be relied upon to be accurate, especially when the radar speed is checked 
against the secondary check.
 
Secondary checks should normally fall within a band of ±10% (plus or minus 10%) of the 
primary reading. This will be a simple pass or fail if the vehicle can be seen to be within the 
band; calculation of an exact speed from the secondary check is not required to be given in 
evidence to support the primary evidence.
8.3    
Typical use
 
Across the road radar speedmeters can be a permanent installation (automatic unattended) 
or portable devices (supervised automatic or attended actively operated).
 
Permanent across the road radar speedmeters are generally unattended automatic devices 
that have some form of secondary check of the vehicle speed that has been acquired by the 
radar speedmeter.
 
Portable devices generally have no secondary check marks on the road, so the speed reading 
must be verified by the opinion of the operator that the speed recorded was consistent with 
what was seen at the time. The operator becomes the secondary check.
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RADAR SPEEDMETERS (ACROSS THE ROAD) 
8.4    
Precautions
8.4.1  
General
 
If the secondary check speed is outside of the aforementioned tolerance then the evidence 
should be examined to determine the possible source of the error.
 
A possible source of error is that the vehicle is either accelerating or decelerating while in the 
field of the radar and secondary check areas. If two or more vehicles are in the secondary 
check area then the evidence should be examined to determine which vehicle is the source of 
the radar speed acquired by the speedmeter. If the vehicle causing the speed reading cannot 
be determined with confidence then the reading should be disregarded.
8.4.2  
Health and safety
 
The operator should always choose a site which affords them and users of the road maximum 
safety with regard to any potential hazard, and must consider the minimum distance a driver 
will  take  to  react  and  come  safely  to  a  standstill  when  stopping  alleged  offenders.  High 
visibility clothing should be worn when the potential for contact with vehicles is possible (see 
chapter 2).
 
Satisfactory operation of the device depends on the correct positioning and alignment of the 
radar. It should be positioned as near to the traffic flow of interest as is convenient.
8.4.3  
Evidence
 
Across  the  road  radar  evidence  from  automatic  devices  is  recorded  by  either  a  ‘wet-film’ 
camera or a digital camera. Evidence from prescribed HOTA devices can be supported by way 
of certification in accordance with Section 20 of the Road Traffic Offenders’ Act 1988. Records 
of the loading and unloading of the film should be recorded for continuity and listed on the 
unused material schedule, providing the record does not undermine the prosecution case.
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GUIDE FOR THE OPERATIONAL USE OF SPEED AND RED-LIGHT OFFENCE DETECTION TECHNOLOGY

PARABOLIC RADAR 
9.1     
Technology description
 
Parabolic  radar  is  used  in  over the  road  speedmeter systems where  the  beam  is  used  to 
illuminate  a  specific  section  of  road;  typically  one  lane  from  equipment  suspended  over 
the surface of the road on a gantry. The system uses the Doppler principle and the Cosine 
correction is calculated to correct the angle at which the system is set to illuminate the road 
surface.
9.2    
Confidence checks
9.2.1  
Alignment
 
Same as across the road radar.
9.2.2  
Distance and speed accuracy
 
Same as across the road radar.
9.3    
Typical use
 
The  most  common  use  is  in  Smart  Motorway  applications  where  the  radar  is  used  in 
conjunction with variable speed limit signs co-located with the speedmeter.
 
Further use of parabolic radars is as virtual loops in place of sub-surface loops in red-light, 
level crossing and speedmeter systems.
9.4    
Precautions
9.4.1  
General
 
Same as across the road radar.
9.4.2  
Health and safety
 
Over the road radar gantries are attended by specialist installation and service engineers; 
untrained personnel should not attend the sites or attempt to service the equipment located 
on such gantries.
9.4.3  
Evidence
 
Over the road radar is largely digital in nature and does not require regular attention other 
than by the manufacturers’ or suppliers’ staff. The evidence is acquired and written to write-
once permanent media for reading in back office IT equipment.
 
Evidence from prescribed HOTA devices can be supported by way of certification in accordance 
with Section 20 of the Road Traffic Offenders’ Act 1988. Records of the loading and unloading 
of the film should be recorded for continuity and listed on the unused material schedule 
providing the record does not undermine the prosecution case.
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10   LASER SPEEDMETERS
10.1 
Laser speedmeter technology description
 
The term laser is an acronym for Light Amplification by Stimulated Emission of Radiation; a 
laser emits light by that process.
 
Light sources, such as incandescent light bulbs, emit incoherent white light from which the 
waves are difficult to steer into a useful narrow beam. Laser light is usually generated in a 
way that causes the light to be emitted in a narrow beam, or the light can be converted into a 
narrow beam with the help of optical lenses. Lasers mostly emit light with a narrow frequency 
spectrum, or more commonly termed as a single colour that scientists call monochromatic 
light.
 
Lasers can use light in the visible or invisible parts of the light spectrum; for practical reasons 
police  enforcement  equipment  uses  invisible  light  in  the  infra-red  spectrum.  It  will  not, 
therefore, interfere with drivers’ or operators’ vision.
 
Laser speedmeters determine speed by shining laser light at a target vehicle in a way that 
illuminates reflective parts of the vehicle. Depending on the reflective properties of the parts 
of the vehicle some of the light is returned to the receiver of the laser speedmeter.
 
By using a series of light pulses the laser speedmeter can, by sensing the movement between 
pulses, be made to calculate the speed of the target vehicle.
 
In operation, laser speedmeters employ sophisticated techniques to measure the quality of 
reflected laser light, as well as predicting when the light will be returned to the device after 
an initial period of acquisition of a target vehicle. It is necessary to reflect light from the 
target back to the laser speedmeter in a predictable and reliable manner. The vehicle’s retro-
reflective surfaces, such as the registration plate, headlamps and rear reflectors are the best, 
but not the only items, to aim at when making a speed reading with a laser speedmeter.
 
Laser speedmeters will typically acquire, quality check, calculate and display the speed of a 
target vehicle in less than 0.5 seconds.
10.2 
Confidence checks
10.2.1   Sight alignment
 
The  sighting  mechanisms  of  laser  speedmeters  are  rigid  and  some  are  adjustable;  the 
adjustment should only be performed at the service centre rather than by an operator. The 
sighting  mechanisms  may  be  checked  for  alignment  through  the  use  of  the  built-in  test 
facility, and it is recommended that verification is carried out before and after each speed 
enforcement session. This is because the less frequently the checks are made, the more days 
of enforcement will need to be cancelled when a defect is found; not because the devices are 
prone to misalignment.
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10.2.2  Distance and speed accuracy
 
Most laser speedmeters are not mechanical devices subject to wear that could cause them 
to drift out of their expected speed accuracy. They are not user adjustable, but for operator 
confidence they may be periodically tested for range or speed accuracy. This should be done 
on a target of known speed or distance, to ensure there has been no change to the instrument 
since it was last calibrated and serviced. The manufacturers’ handbook should give details of 
this type of check.
10.3 
Typical use
 
Laser speedmeters are typically used as hand-held or tripod mounted devices; all of which 
are attended actively operated devices.
 
The  speedmeter  is  aimed  at  the  target  vehicle  at  the  front  or  rear,  with  the  illuminating 
beam being made to cover as many retro-reflecting surfaces as possible. For example, the 
registration plate, lights or light covers and rear-reflectors.
 
The vehicle will need to be tracked with the aiming sight to allow sufficient reflected light to 
return to the receiver to make a speed measurement.
 
The operator is not restricted in his choice of target, only measuring vehicles which he has 
already assessed to be exceeding the speed limit, but must assess any reading obtained and 
compare it with his own view of the apparent speed of the vehicle as it was being measured.
10.4 
Precautions
10.4.1   General
 
Laser speedmeters must not be used through glass or plastic screens to avoid diffraction 
or scattering of the laser beam. While vehicle screens pass light with minimum diffraction, 
elements within vehicle screens, as well as their cleanliness, makes the path of laser light less 
predictable so it is discouraged in law enforcement devices. They can be used from within 
vehicles through an open aperture, such as a window.
 
Take care that lenses are not damaged or dirty by not placing the instrument in a position 
where this can occur. Make a visual inspection of the equipment for damage before use.
10.4.2   Health and safety
 
The  output  power  of  laser  speedmeters  is  required  to  be  in  the  Class  1  (eye-safe) 
recommendations as laid down in British Standard BS EN 60825-1: 2001. In addition users 
should  not  point  the  devices  into  a  person’s  eye  at  short  range  and  for  a  long  period  of 
time. Use for the measurement of vehicle speed will not present a hazard to anyone in the 
transmitted light beam.
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10   LASER SPEEDMETERS
10.4.3   Evidence
 
Handheld  devices  not  producing  a  record  –  the  speed  of  the  target  vehicle  should  be 
noted on all occasions that a speed measurement is taken which exceeds the speed limit in 
which enforcement is taking place by the intended margin for that enforcement. The range 
measurement may also be noted if the circumstances allow a note to be made of the range.
 
Devices which produce a record – no separate note need be made of the speed of the target 
vehicle.  The  record  will  be  the  primary  evidence  of  speed  and  range  and  the  role  of  the 
operator is to verify that reading at the time it was made by making an assessment as to 
whether the apparent speed of the vehicle corresponded to that reading. If it did not, then 
enforcement should cease until the device has been checked.
10.5 
Laser speedmeter check range
10.5.1   Description
 
A range of known distance between a marked target and operating point can be constructed 
to carry out periodic confidence checks.
 
A mark should be made on the ground or by a fixed object to allow accurate positioning of the 
laser speedmeter (the operating position) when it is to be tested. A target marked with paint, 
a road sign or other flat object should be placed in a fixed position and oriented vertically so 
the laser speedmeter can be aimed to cause a reflection back to its receiver. When correctly 
positioned the laser should confirm the known distance to the target and, in some cases, 
confirm a speed of 0mph for the test target.
 
A note can be made of the results of the check either in a pocket note book, a statement or 
in a log book that is kept with the equipment.
10.5.2   Range set-up
 
Decide on a safe location with an uninterrupted laser targeting line between the aiming point 
and the target.
 
Measure the distance between the aiming point and the target with either:
1  Two laser speedmeters (both must agree)
2  A calibrated measuring wheel
3  A steel rule or steel tape rule
4  Another distance measuring device with established accuracy
 
Note the distance and record the evidence of the range set-up or measurement in a statement 
form for later use in court.
 
Officers can check an existing range using any of the methods above so that they can evidence 
the details of the range measurements themselves in a statement, if required to do so in 
court.
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11    SITING CONSIDERATIONS FOR AUTOMATIC 
UNATTENDED SPEEDMETERS
11.1 
Site surveys
 
The following should be considered as good practice when installing any fixed sites for the 
unattended use of HOTA enforcement technology:
•   Sites where radar or laser installations are being considered should be examined to avoid 
any large reflective surfaces, such as street signs in the path of the measurement beams
•   Radio Frequency Interference (RFI) checks should be considered at all laser and radar sites 
where radio interference may be of concern, to ensure no interference is present and 
records retained as part of a site file
11.2 
Unattended site set up
•   For  all  unattended  sites,  photographic  records  covering  a  360  degree  view  of  the  site 
should be taken and retained for future reference in case of site changes. These reference 
images should be periodically checked to ensure no installations have been completed at 
sites that may interfere with the device
•   Evidence produced from unattended sites should have either a secure site location ID on 
as part of the evidence produced, or a mark on the road surface that appears in the image 
to identify the location
•   Where the location of a device is such that the site can be clearly determined within the 
image, ie a road where permanent features such as buildings or road junctions appear in 
the image, then no markings or electronic ID will be necessary
•   Where  the  location  is  on  a  motorway  and  no  physical  features  exist,  markings  or 
automatically programmed electronic ID should be provided such as GPS coordinates
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12   IN-CAR DISTANCE/TIME DEVICES
12.1 
Technology description
 
The detection of speeding offences using the equation:
Speed = Distance divided by Time
 
This is a long established practice, initially carried out by the use of a certified stopwatch 
and the odometer of the patrol car. While this principle remains, technology has allowed for 
the introduction of sophisticated equipment, which has proved to be far more efficient and 
accurate. The operation of the devices simply involves the operation of a distance switch and 
a time switch, in the appropriate sequence. This calls for a high level of operator accuracy 
and, in order to achieve it, appropriate training is required.
 
Where a vehicle is, in the opinion of a police officer, travelling at an excessive speed the 
device is used to corroborate that opinion.
12.2 
Confidence checks
12.2.1   Sight alignment
 
There  are  no  alignments  of  sights  required  with  this  type  of  equipment,  however,  some 
equipment is supplied with a video camera that should be aligned to the vehicle being 
checked at the time the record is made.
12.2.2   Distance and speed accuracy
 
Because  these  devices  rely  in  part  on  the  mechanical  components  of  a  vehicle,  which 
are  subject  to  wear,  these  devices  must  be  regularly  calibrated  in  accordance  with  the 
manufacturers’ instructions. Full calibration must be carried out:
1  On initial installation,
2 Following removal and reinstatement,
3 Following the fitment of new tyres, and
4 At weekly intervals
 
In order to establish the on-going accuracy of the device all of those listed above should be 
recorded in a log book for the device with the identification of the officer calibrating being 
made clear.
 
If the device is found to be inaccurate the defect must be remedied and any offences detected 
since the previous accuracy check should be reviewed; as it may not be known at what point 
the equipment became defective.
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12.3 
Typical use
12.3.1   Overview
 
The checking of a target vehicle’s speed can be done by checking its movement between two 
references, either permanent or temporary, on or near the carriageway, such as:
 
•  a moving shadow on a stationary object or a mark on the road surface
 
•  a moving object on a stationary shadow or a mark on the road surface
 
•  a shadow-to-shadow contact
 
•  physical contact of vehicle wheels with reference point
 
•  when both vehicles are side by side
 
By using reference points that fit this, or are similar to this definition, any uncertainty can be 
eliminated.
 
It is important to remember the police vehicle must pass between the same points as the 
target vehicle. This is essential as the distance information is taken from the police vehicle.
 
When  the  police  vehicle  has  travelled  between  the  two  points  and  the  distance  switch 
operated, on at the first point and off at the second point, the device then knows the distance 
between the points. As the target vehicle travels between the same two points, the time 
switch is operated. The time switch is switched on at the first point and off at the second 
point. The device now knows the time the target vehicle took to travel between the two 
points.
 
The  device  now  has  both  parts  of  the  equation  required  to  calculate  the  target  vehicle’s 
average speed. This is done in a fraction of a second and the result is then visible on a digital 
display.
 
If, for any reason, the operator has any doubt as to the validity of the check, it must be 
abandoned.
12.3.2  Follow check
 
This  type  of  check  is  carried  out  when  the  police  vehicle  is  following  the  target  vehicle. 
As  the  target  vehicle  passes  the  first  reference  point,  the  time  switch  is  turned  on.  As 
the  police  vehicle  passes  the  same  reference  point,  the  distance  switch  is  turned  on. 
As  the  target  vehicle  passes  the  second  reference  point,  the  time  switch  is  turned  off. 
 
The device now knows the time the target vehicle took to travel between the two reference 
points. As the police vehicle passes the second reference point, the distance switch is turned 
off. The device now knows the distance between the two reference points that the target 
vehicle has travelled.
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12    IN-CAR DISTANCE/TIME DEVICES
12.3.3   Pre-fed distance check
 
This type of check is carried out when the police vehicle travels between the two reference 
points. Turn the distance switch on at the first point and off at the second point.
 
The police vehicle then parks in a position that the two reference points can be clearly seen 
by the operator.
 
The device has the distance between the reference points stored. As a target vehicle passes 
between the points the time switch is turned on and off. The device can then calculate the 
speed. Providing the distance information is not cleared from the device the police vehicle 
can remain parked and, by clearing the time information only, another target vehicle can be 
checked.
12.3.4   Being followed check
 
This check is carried out when the police vehicle is travelling in front of the target vehicle that 
is approaching from behind at a speed which is excessive.
 
The police vehicle will travel between the two reference points, with the operator turning the 
distance switch on and off. The device now knows the distance travelled.
 
As the target vehicle, still approaching from the rear, passes the same points the time switch 
is turned on and off. The device now knows the time taken to travel between the reference 
points. The device knows the distance and time and can calculate the speed.
12.3.5  Crossing check
 
This check is started when the police vehicle is stationary.
 
As the target vehicle passes the first reference point, the time switch is operated. The police 
vehicle then moves off behind the target vehicle, operating the distance switch as the police 
vehicle passes the same reference point.
 
With the police vehicle now following the target vehicle and both time and distance switched 
on, the completion of the check is the same as the ‘follow check’.
12.3.6   Dial in distance check
 
This mode enables a known distance previously measured by the device to be fed into the 
device computer without the need to drive again over the route. Record the distance on the 
same push button switches as used for calibration purposes. This procedure can also be used 
with the control module removed from the car and plugged into the portable battery pack.
 
Particular care must be exercised where shadows are used as these will change with the 
movement of the sun.
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The minimum distance for any check is generally 1/8 or .125 of a mile. However, checks over 
a shorter distance, down to an absolute minimum of 0.07 of a mile, are permissible under the 
following circumstances:
a.  This minimum distance is only for pre-fed or dial in distance checks
b.  The  reference  points  at  both  the  start  and  end  of  the  check  are  permanent  physical 
features on or close to the road surface, which provide a clear and visual reference
c.  The maximum speed limit at the site does not exceed 40mph 
 
Trainers are to be satisfied that operators carrying out reduced distance checks are capable 
of performing the function accurately.
12.4 
Precautions
12.4.1   General
 
Police radio transmitters, whether hand-held or car mounted, must not be used at the moment 
a vehicle speed is being measured. Turn off the in-car and personal radio equipment or set 
to ‘transmit inhibit,’ where available, for the duration of the speed measurement unless the 
device is Home Office Type Approved and is shown to be unaffected by radio interference.
12.4.2   Health and safety
 
When checks are being made at high speed it is necessary to operate the controls of the 
device at the same time as the vehicle is being driven. Care should be taken to ensure that 
the operator/ driver is familiar enough with the equipment controls so the operation of the 
device does not become a distraction to the maintenance of safe vehicle control.
12.4.3   Evidence
 
Distance/time device evidence is the speed, time and distance records which should all be 
noted by the operating officer. If an approved video or data logging device is fitted to the 
distance/time device, this may be used as the record from the device.
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13   AUTOMATIC DISTANCE/TIME DEVICES
13.1 
Technology description
 
This type of speedmeter system uses the distance/time method of average speed calculation; 
the  speedmeter  being  pre-fed  with  the  distance  between  the  entry  and  exit  points,  the 
‘baseline’ with cameras at the same points detecting vehicle identification data, along with an 
accurate time that the data is collected. The vehicle data and time information is transported 
to a matching system where the entry/exit data is used to calculate the average speed of the 
vehicle as it transits the known distance between points of data collection.
 
The  components  of  the  system  are  connected  by  a  dedicated  or  public  communications 
channel,  with  data  integrity  being  assured  by  encryption  when  public  communications 
channels are used.
 
The data collected for an offence is written to write-once media before transfer to a back 
office facility for adjudication purposes.
 
The  system  shows  the  minimum  speed  between  the  entry  and  exit  points  because  the 
baseline is required to be set at the minimum possible driving distance between those two 
points.
13.2 
Confidence checks
13.2.1   Site alignment
 
Automatic distance/time devices have their video imaging systems set to a locked position 
from which the baseline reference is taken. It is required, therefore, that after commissioning 
and calibration the camera supplying the video image does not move. To assure that the 
camera  has  not  moved  between  calibration  periods  and  an  offence,  a  permanent  mark 
visible to the camera system should be made on the road surface with the position of the 
mark being visible in the offence overview image. An overview image from the entry and 
exit positions should be provided along with the calibration certificate for the device. The 
calibration images should be used as reference images, with the visible marks in the offence 
images being compared to them to assure that no movement of the cameras detecting the 
target vehicles has occurred between the time of calibration and the recording of any offence. 
There is no requirement for a site number or any other identifying mark to be provided at the 
site but this is not precluded.
13.2.2   Distance and speed accuracy
 
The distance between the entry and exit point should be measured with a calibrated distance 
measuring device; the distance being measured a minimum of three times, with each of 
the results being within 1% of the average of the three measurements. The shortest of the 
three measurements is then taken as the distance between the points for the average speed 
calculation. The baseline length shall be measured using a calibrated surveying instrument, 
such as a theodolite, total station, measuring wheel, steel tape, surveyor’s chain or, where 
there is no restricted view of the sky throughout the length of the base line, with a vehicle 
mounted GPS system acceptable to CAST or another method acceptable to CAST.
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A drive through test can be performed to show accuracy, but this is not a requirement of this 
type of system. 
13.3 
Typical use
 
The  system  can  be  configured  in  a  point-to-point  arrangement  or  be  arranged  for  area 
coverage  in  a  multipoint-to-multipoint  arrangement;  the  latter  arrangement  allowing  any 
camera to any camera operation on multiple baselines.
13.4 
Precautions
13.4.1  General
 
It is essential that the baselines are correctly identified for each location before enforcement 
commences.
 
In  roadworks,  where  frequent  changes  to  the  road  layout  between  the  entry  and  exit 
cameras are possible, the baseline must be re-established for each affecting change with a 
new calibration certificate being issued by the system supplier or agent.
13.4.2  Health and safety
 
There are no specific health and safety precautions for this type of equipment.
13.4.3   Evidence
 
Evidence  is  written  to  a  write-once  permanent  medium  for  transfer  to  a  back  office 
adjudication system. A print of the evidence of the back office system should be certified 
with a Section 20 certificate for presentation in prosecution files. A statement or calibration 
certificate evidencing the baseline length between cameras should be kept but will normally 
be placed on the unused material schedule.
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14   CHRONOMETERS
14.1 
Technology description
 
Several types of chronometer were approved by ACPO for use in detecting offences of excess 
speed. They function by having a known distance pre-fed into them, and the time taken for 
the target vehicle to cover that distance is then measured in the same manner as a pre-fed 
check or dial in distance check using time/distance devices.
 
Since the operator has no means of checking the accuracy of the distance used, chronometers 
should only be used at locations where:
1  The distance has previously been measured and is verifiable to within 1% of the distance 
between points, and
2  Both reference points to be used in the check are permanent marks or features clearly 
visible to the operator
14.2 
Confidence checks
14.2.1   Sight alignment
 
None required.
14.2.2   Timing check
 
The timing accuracy of chronometers should be checked periodically to show that the timing 
is performing adequately.
 
The timing accuracy can be checked against another timing source to show that there are no 
gross errors in the enforcement equipment; this can be achieved by checking the device over 
a period of a minimum of two minutes with the readings required to be within one second of 
each other.
 
Suitable timing sources are:
1  A speaking clock on a telephone service
2  A timing signal received via a radio service
3  A Home Office Type Approved device that provides timing to a resolution of one second
 
It is recommended that a log book is kept with the equipment where a record of the checks, 
who performed them and what reference was used are noted.
 
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14.2.3   Distance and speed accuracy
 
The distance between the entry and exit point should be measured with a calibrated distance 
measuring  device;  the  distance  being  measured  a  minimum  of  three  times  with  each  of 
the results being within 1% of the average of the three measurements. The shortest of the 
three measurements is then taken as the distance between the points for the average speed 
calculation. The baseline length shall be measured using a calibrated surveying instrument, 
such as a theodolite total station, measuring wheel, steel tape, surveyor’s chain or where 
there is no restricted view of the sky throughout the length of the baseline, with a vehicle 
mounted GPS system acceptable to CAST or another method acceptable to CAST.
14.3 
Typical use
 
The chronometer is operated from a vantage point with the operator observing the traffic to 
be measured from within a vehicle or a roadside position.
14.4 
Precautions
14.4.1   General
 
Electronic chronometers should not be operated in the presence of transmitting police radios.
 
‘Transmit  inhibit’  should  be  enabled  when  carrying  out  speed  checks  with  this  type  of 
equipment.
14.4.2   Health and safety
 
Normal roadside precautions should be observed.
14.4.3   Evidence
 
Evidence of the speed reading should be recorded by the operator at the time the speed 
measurement is made.
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15   SENSOR OPERATED ROADSIDE SPEEDMETERS
15.1 
Technology description
 
These devices typically offer a method of checking vehicle speeds on the road by the use of 
either electrical Piezo Co-Axial cables, or hollow rubber tubes fixed across the carriageway at 
right angles to the flow of traffic.
 
The sensors are set at a specified distance apart, and the instrument measures the time 
taken to cover that distance between the sensors, then computes the average speed of the 
vehicle.
 
The piezo sensors may be embedded in housings set in the road surface, with connecting 
cables leading from these permanent sensors to a post at the roadside where the speedmeter 
can be connected or to fixed speedmeter systems.
 
With piezo-electric and hollow-tube types of sensor, the pressure of the vehicle’s road wheels 
passing over it is converted into an electrical pulse used to stop and start timing counters in 
the device. The values captured are used to calculate and display the average speed.
15.2 
Confidence checks
15.2.1   Alignment
 
Fixed sites will have cameras aligned to the road but the alignment angle does not affect 
speed accuracy.
 
Mobile sites will require alignment of any camera system to ensure target vehicle data is 
correctly captured.
15.2.2   Distance and speed accuracy
 
The accuracy of these systems is dependent upon the distance between the sensors and the 
clock accuracy in the attached equipment.
 
For temporary installations, such as mobile systems with pneumatic tubes installed by an 
operator, the tubes must be installed accurately to the template or measurements supplied 
in  the  manufacturers’  handbook.  Temporary  installations  should  be  checked  by  driving 
through the system with a vehicle, of which the speed is verified by the use of another HOTA 
speed measuring device before enforcement takes place.
 
Permanent sub-surface installations should be checked by the supplier, either annually or 
once every two years. A drive-through check is recommended at the first commissioning or 
after replacement of the sensors.
15.3 
Typical use
 
Sub-surface sensors are used for fixed and mobile speedmeter operations. Pneumatic sensors 
are used for temporary mobile systems only.
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15.4 
Precautions
15.4.1   General
 
Operators must be aware of the potential for certain axle configurations to create artificial 
readings.  Compliance  with  proper  operating  procedure  will  ensure  no  inappropriate 
prosecutions are mounted.
 
Where sensor deterioration is observed a drive through check can be carried out at intervals 
to assure speed accuracy is maintained.
 
Where serious damage is observed the speedmeter should be taken out of service and the 
supplier or agent should be contacted for repairs to be carried out.
15.4.2   Health and safety
 
All  operators  setting  up  sites  will  wear  high  visibility  clothing  at  all  times.  Safety  goggles 
should be worn when nailing sensor fixings into the road surface. Operators should ensure 
that such fixings do not cause danger to other road users and are removed at the end of the 
check.
 
It is important that a sufficient and safe stopping distance is allowed between the check site 
and stopping officers. Distances will vary according to differing site features and weather 
conditions. Stopping officers will wear high visibility clothing at all times.
15.4.3   Evidence
 
For temporary mobile sites, the site must be selected so that the operator is in a position 
to form an opinion that the target vehicle is exceeding the speed restriction for that road. 
Unless the device has an approved secondary check, the speed registered on the device only 
corroborates the operator’s opinion.
 
The speed registered by mobile systems should be recorded at the time of the offence unless 
there is an approved data recording system attached to the speedmeter.
 
Fixed sites have either a wet-film record or a digital data storage system.
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16   CAMERAS
16.1 
Technology description
 
This  section  deals  with  evidence  and  records  made  from  video  or  camera  attachments 
approved as part of, or for optional use with, specified HOTA and ACPO approved devices.
 
The devices in these combinations of equipment may be used separately where approval for 
such separate use has been given.
 
The absence of a camera will in no way affect the Type Approval of the device should non- 
photographic operation be decided upon. Where a camera is attached to a HOTA device, the 
camera must have HOTA for use in conjunction with that particular device.
 
If a camera attachment is used for recording purposes in the attended mode, one photograph 
will  suffice  provided  it  incorporates  all  relevant  data  including  the  speed  reading,  as  the 
device only corroborates the witness’s opinion. However, where a device is used with a HOTA 
video recording device, the full record will be the moving image showing the targeting and 
measurement of the device.
 
If the device is Type Approved for unattended automatic use, any camera will form part of the 
HOTA device and will be used in conjunction with an approved second independent method 
of speed measurement. This secondary check is required in order to provide a further check 
on the accuracy of the device. No secondary check is required for red-light cameras since 
the two images required by Type Approval provide sufficient check on the movement of an 
offender’s vehicle.
16.2 
Confidence checks
16.2.1   Site alignment
 
Roadside  furniture  and  equipment  must  be  installed  in  accordance  with  manufacturers’ 
instructions and relevant highway safety legislation.
 
Care should be taken to ensure that the presence of the equipment does not create a road 
safety  problem  and  that  road  signs  and  the  like  are  not  obscured,  or  their  effectiveness 
diminished by the equipment.
 
Care should be taken to ensure the camera housing is not obscured by signs or foliage to 
prevent the obscuration of evidence acquired by the system. Visibility of the camera housing 
will also have the benefit of deterring the use of excess speed by passing motorists.
 
The use of dummy flash units should receive favourable consideration, as experience has 
shown they have a deterrent effect and are an excellent accident prevention factor.
 
Experience has further shown that one camera circulating between up to a maximum of ten 
sites, and moved at regular intervals, will produce an effective casualty reduction result.
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16.2.2   Distance and speed accuracy
 
HOTA unattended automatic devices will have a second independent method of checking 
the primary speed measurement. One such method offered by manufacturers is the taking 
of two photographs of the offending vehicle at a known time apart, which can be compared 
with the distance travelled within that time interval to arrive at the speed of the vehicle. Only 
approved methods of secondary checks should be utilised.
 
A survey of each site by the manufacturer or agent where an unattended automatic device is 
to be located must be carried out to ensure its suitability with regard to the manufacturers’ 
instructions.
 
Before  enforcement  activity  commences  each  installation  will  be  the  subject  of  a 
commissioning procedure at which the police should be present or the police should verify 
afterwards. The record of that commissioning will be retained for evidential purposes in case 
the integrity of the site is questioned.
 
Any alteration in the configuration of the site will require the site to be recalibrated. Great care 
should be taken to ensure secondary check marks are replaced accurately after resurfacing 
work.
16.2.3   Evidence
 
Evidence from HOTA speedmeters can be recorded by way of visual information recorded 
that shows the scene of the speeding offence, as well as having the imprint of the offence 
data upon the image.
 
Wet-film cameras are required to have an imprint of the offence data on the image.
 
Digital images are not required to have an imprint of the offence data on the image of the 
offence; the offence data being verified by the equipment at the time of the offence and in 
subsequent recording.
 
Images produced by automatic unattended devices may be used to verify the primary speed 
measurement by way of providing a secondary speed band that is at or within 10% of the 
primary speed measurement.
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17    RED–LIGHT ENFORCEMENT CAMERAS
17.1 
Technology description
 
Automatic camera systems have been developed that can detect when a vehicle has failed to 
comply with a traffic sign, particularly traffic signals or traffic lights and the relevant stop line.
 
Examples of such systems are junctions controlled by traffic lights and level crossings over 
railway lines controlled by flashing stop signals. The systems for junctions and level crossings 
are broadly known as red-light cameras.
 
The systems can be Home Office Type Approved to make evidence from them admissible 
by way of a certificate produced under Section 20 of the Road Traffic Offenders’ Act 1988, 
containing or accompanying the record from the device.
 
The majority of approved systems detect the position of a vehicle with loops or piezoelectric 
strips buried beneath the surface of the road immediately before and immediately after the 
relevant stop-line. Vehicle presence detectors such as radar, laser or video camera systems 
using  Automatic  Number  Plate  Recognition  (ANPR)  can  also  be  used  to  detect  vehicle 
positions in relation to the stop line.
 
The camera systems are activated by detection of the status of the traffic signal. Violations 
are detected only after an interlock is completed from the detection of the red-light being 
illuminated in the relevant traffic signal head, to assure courts that the red-light was showing 
as the driver approached the traffic signal.
 
After  a  pre-determined  delay  time  between  the  amber  and  red  signal  lamps  becoming 
illuminated, vehicles passing the detectors will have one image taken as they pass over the 
stop line and a second after they have continued past the position shown in the first image.
 
The  images  from  automatic  red-light  cameras  have  within  the  first  overview  image  the 
relevant traffic signal head so the illumination status of the green, amber and red lamps at 
the time of the images and the vehicle passing over the stop line can be evidenced. There is 
also a specific time for which the amber must be illuminated before changing to red. This is 
three seconds, plus or minus a quarter of a second, and the actual illumination time of the 
amber will be contained within the data block to confirm compliance with this requirement.
 
Red-light camera equipment may, in addition to the position of the vehicle, show an indication 
of the minimum speed of a vehicle as it has crossed the stop line and the time since the red-
light has become illuminated. Red-light cameras which display a speed are tested during Type 
Approval for accuracy of that speed reading to the same tolerance as a speed camera, but are 
permitted to display a speed reading “in excess of” a certain figure if they cannot be accurate 
to the required tolerance above that figure.
 
The speed can properly be taken into account when setting conditional offer and prosecution 
thresholds, but currently when operating in red-light mode, the device is not simultaneously 
operating as a speed camera. Therefore, a prosecution for speeding cannot be based solely 
on this measurement.
 
The requirement that interlocks are satisfied, the offending vehicle is shown in images before 
and after the stop line is crossed and the requirement to show the status of the red lamp in 
the images, creates a certainty the vehicle identified in the violation record has committed 
the breach of the stop line.
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It is not necessary to make regular checks of the degree of accuracy of the red-light camera 
beyond the recommended certification period stated by the device manufacturer or agent.
 
Stop line detection systems can be used or combined with speed detection systems, with 
functions switched between stop line detection and speed detection being changed by the 
status of the traffic signals.
 
‘Speed-on-green’ camera systems are a typical example of a combined device.
17.2 
Confidence checks
17.2.1   Red-light in offence image
 
There is no requirement for commission checks beyond what the manufacturer carries out in 
the annual checks and calibration of the device.
 
It  is  recommended  that  the  evidence  in  each  offence  detected  is  examined  to  check  the 
red-light is illuminated and in view when the stop line was crossed, and that no other light is 
illuminated with the red. If the stop line is obscured (e.g. by snow) then the default position 
is that the vehicle must not pass the post on which the red-light is mounted. This should also 
be visible in the photograph.
17.3 
Typical use
 
These systems are used at traffic light junctions and railway crossings with one or more lanes 
of traffic. Cameras are arranged so the stop line and the traffic signal head and the vehicles 
travelling past the stop line are visible in the record.
17.4 
Precautions
17.4.1   General
 
Loops and piezo-electric detectors at traffic light junctions are susceptible to wear of the 
surface  of  the  road.  Any  wear  detected  that  results  in  the  detectors  becoming  exposed 
should be reported to the device supplier and the use of the device suspended until repairs 
are completed.
17.4.2  Health and safety
 
When installing portable cameras care should be taken to ensure approaching traffic is able 
to see operators servicing the camera systems so collisions are avoided.
 
Installation of fixed equipment at or near railway crossings should be done in a way that 
prevents the need for access to the railway to install and remove portable equipment.
17.4.3   Evidence
 
The images from the device will show the position of the vehicle as it crossed the stop line 
and after the line has been crossed; in cases that are to be heard in court both images should 
be served in the record from the device. The images forming the record from a Home Office 
Type Approved device will be admissible when covered or contained within a Road Traffic 
Offenders’ Act 1998 Section 20 certificate.
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