Motorway Incident Detection and
system is saving: Fatal accidents saved
Frequently Asked Questions
Automatic Signalling MIDAS
per year 17
Serious injury accidents saved per year 84
Q:
Why are signals set and there
The MIDAS system automatically detects
Slight injury accidents saved per year 686
seems to be no queue?
queues by monitoring the speed of
Damage only accidents saved per year
vehicles passing detectors spaced at 500
6,006
A:
Once set, automatic signals remain
metre intervals.
Value of accident savings per year £74
set for a minimum of 2 minutes to
million (2006 prices)ii
avoid giving rapidly changing
information to the motorist.
Congestion management for SMART
Operators in the RCC can override
motorways
these settings if required.
These areas of motorway have additional
Q
What causes queues, doesn’t
Loop
processing to actively monitor traffic flows
traffic simply regulate itself?
and speeds to detect the onset of
congestion, speeds are progressively
A
There are small variations in
reduced as congestion increases. This
speeds between vehicles, as traffic
slows vehicles and helps preserve smooth
density increases bunching of
flow for longer. These measures improve
vehicles occurs. The One Show
journey time reliability, delay the onset of
with Southampton University
MIDAS measures the amount of time a
peak time congestion and when traffic
carried out an experiment which
loop is actuated by a vehicle passing over
volume reduces the motorway returns to
can be viewed here
it and can therefore detect slow moving
free flowing conditions more quickly.
https://www.youtube.com/watch?v=
traffic.
Rryu85BtALM
Once slow vehicles are detected speeds
Queues can also be due to lane
of 40 and 60 are set and to compliment
changing behaviour or a lane
these roadside signs are set with queue
restriction (i.e broken down
ahead and queue caution messages.
vehicle).
Reducing speed smoothes traffic flow and
reduces stop / start traffici.
MIDAS has been modified to
reduce sensitivity to where one
MIDAS covers 1,513 kilometres of route.
slow moving vehicle, such as a
Research on the benefits of MIDAS
Wide Load, passed over the loops
carried out by the Transport Research
and triggered speed restrictions.
Laboratory in 2006 it is estimated the
Page 1 of 3
Q:
What conditions are required to set
Protection system is installed for
In a relatively small number of
the speed limits?
safety reasons to help prevent
cases, there could be a fault with
motorists arriving at the back of a
the system and it is very helpful
A:
40 is set when traffic downstream
queue whilst still travelling at 70. If
when motorists notify the Customer
is detected travelling over a loop
the queue is still there, then the
Contact Centre so that potential
for 2 seconds or longer, for cars
signals will still display 40. The 40
problems can be investigated.
this is typically around 8MPH.
is not a target speed, it is a
Further upstream a 60 will then be
maximum allowed speed. Once
Q:
Why is there a 2 minute minimum
set to progressively smooth traffic.
traffic starts to move, this speed
time for signal settings?
In smart motorways there is further
restriction will aid the slow moving
processing that will set 50 when
body of traffic to pick up speed
A:
The signals remain on for a time
average speeds of 30MPH or less
generally before allowing higher
after a queue has started to
are detected. Smart motorways
maximum speeds, reducing
dispense to ensure a smooth
can also be set up to set 50 &
stop/start driving.
transition to free-flow conditions
60MPH speed limits in response to
and reduce the bunching that
congestion by setting flow
Q:
Are there any improvements
causes queues.
thresholds linked to locations that
planned?
cause congestion to build rapidly.
Q:
I’m sure that MIDAS causes
A:
Highways England is constantly
congestion!?
Q:
Why do we get signals set to 40
sponsoring research into
one after another?
improvements. This covers
A:
Extensive analysis has been done
everything from replacement
by the Transport Research
A:
This is to advise the motorist that
detectors for the loops in the road
Laboratory into the day to day
further queuing traffic is ahead.
to improved visibility of signals and
operation of MIDAS. This includes
Queues are often not uniform –
signs. In addition, improved
comparisons of congestion and
there can be a section of halted
maintenance techniques have
queues on stretches of similar
traffic, followed by a clear stretch of
been introduced to increase
motorways with and without
road, then another section of slow
reliability.
MIDAS. In all cases, it has been
moving or stopped vehicles.
conclusively demonstrated that
Q:
Do other countries have MIDAS?
MIDAS improves journey time
Q:
Why is 40 still displayed when I am
reliability, smoothes traffic flow and
stopped?
A:
Similar systems are in widespread
reduces accidents.
use throughout the world. The
A:
The automatic systems cannot set
New Zealand Roads Authority
lower speeds than 40. The Queue
have a number of information
Page 2 of 3
videos explaining how smart
motorways work.
ii Tucker, S., et al., (2006) Evaluating the benefits
Q:
I often see 60, 50, 40, 60, 50, 40 is
of MIDAS automatic queue protection in Traffic
the system working correctly?
Engineering and Control.
A:
The speeds set are in response to
Traffic plot showing queues (white streaks of slow
traffic) moving backwards along the motorway.
traffic conditions downstream and
designed to progressively reduce
speeds as the back of the queue is
approached. Queues move
backwards along the motorway in
waves. Under some traffic
conditions, when a 40 is set it
creates a smaller wave which on a
smart motorway will trigger the
intermediate 50. Reducing the
minimum on time from 4 minutes to
2 minutes has increased the
incidence of this by making the
system more responsive to traffic
conditions.
i Duncan, N.C (1979),
A further look at speed/flow/concentration in
Traffic Engineering and Control 20(10), 482.
Lighthill, M.J., and Whitham, G.B., (1955) On
kinamatic waves II: a theory traffic flow on of
crowded roads, Proceedings of the Royal Society,
229(1178), 317- 345
Hall, F.L., and Montgomery, F.O., (1993) The
investigation of an alternative interpretation of the
speed-flow relationship on UK motorways in
Traffic Engineering and Control, 34(9).
Mathematicians take aim at ‘phantom’ traffic jams
Page 3 of 3