This is an HTML version of an attachment to the Freedom of Information request 'London Underground station delays'.

Incident Data Guidance Note 
 
Limitations of the data 
 
The data in the associated file represents a snapshot of the data set at the time it was 
extracted. 
 
It is not uncommon for the incident details to change as further investigations are carried out.  
Sometimes investigations may take several weeks to complete, depending on the complexity 
of the incident. 
 
 
Definitions 
 
The following gives definitions for the data headings used in the associated file. 
 
Line 
The London Underground line (e.g. Victoria line) on which customers were delayed by an 
incident. 
 
Date 
Date incident occurred. 
 
Time 
Time the incident initially occurred at. 
 
Day 
Day of the week. 
 
Location 
Location the incident occurred at based on where customers were delayed. 
Note: Not all incidents occur at a specific station, with some delays occurring when a train is 
in between stations.  In these scenarios, depending on exactly where the train is in the 
section the incident may be booked to the station the train is departing from, or the station 
the train is delayed arriving to. 
 
Direction 
The direction the train was travelling in when an incident occurred. 
Note: This field only applies to trains in passenger service on the running line.  Therefore if a 
train has been cancelled in the train depot without entering service this field will show as 
“N/A”.  Similarly if the incident refers to the business function of “Stations” involving assets 
such as lifts or escalators the direction will also show as “N/A”. 
 
Initial Delay 
The number of minutes the train service is initially delayed for due to an incident. 
 
Example: A customer is taken ill on a train and is helped off by station staff.  The train is 
delayed departing by three minutes, and therefore the initial delay is three minutes. 
 
 
 

Total Duration 
 
Whilst initial delay only captures the initial delay to the train service, the total duration 
captures the full extent of an incident if it is more than a simple stop / start. 
 
The total duration could reflect: 
•  The total time a train is missing from service after being withdrawn, with the time a 
replacement train enters service being the time the duration finishes. 
•  The total time a signal fault took place over, with the time the signal is fixed and 
returning to normal operations the time the duration ends. 
 
Example 1: A train is withdrawn from service due to a defect at 20:00.  The initial delay to the 
train service is five minutes, but the train itself is taken out of service for three hours whilst 
the fault is fixed, re-entering service at 23:00.  The total duration is based on the time 
between the initial incident occurring, and the train re-entering service.  In this example the 
duration would be 180 minutes. 
 
Example 2: A signal failure occurs at 13:00 causing a five minute initial delay to the first train.  
However the signal continues to fail and is not fixed until 14:00.  In this example the duration 
would be 60 minutes. 
 
Example 3: If multiple trains are missing from service for the same reason the disruption 
maybe booked as multiple cancellations under one incident.  This has been used regularly 
for lack of train operators due to COVID19.  These incidents will appear with an initial delay 
of 0, but often a high figure for the duration.  If 10 trains are missing from service for 10 
hours each, this would be shown by a duration of 6000 minutes (based on 10 trains x 600 
minutes). 
 
 
 

Business function 
 
Business function is used to describe the different departments in London Underground.  
Each incident is assigned a business function based on the root cause responsible for the 
train being delayed, withdrawn or cancelled.  A brief summary of these is explained below: 
 
Business Function 
Description 
Four Line 
Four Line Modernisation involves the upgrading of trains, 
Modernisation (4LM)  signalling, and power across the Metropolitan, District, Circle, and 
Hammersmith & City lines.  These incidents are related to the 
upgrade work. 
Customer Service 
Incidents involving customers such as a train being delayed due to 
an ill customer being taken off the train, or a train being stopped 
short due to a member of station staff using a track retrieval device 
to pick up a customers dropped mobile phone from the track. 
Fleet 
Any incident involving a train being delayed, withdrawn or 
cancelled due to a defect on the train. 
Line Operations 
Refers to incidents predominantly involving train operators such as 
a train being cancelled due to lack of available train operators. 
Other 
This is used to capture other categories including delays due to:  
•  Network Rail infrastructure such as non London 
Underground signalling; 
•  Safety and security – such as police asking a station to be 
closed due to a criminal offence taking place outside the 
station; 
•  Extreme weather related incidents – one off events. 
•  Power failures due to UK Power Network 
Power 
Any incident involving a power failure where the power supply is 
provided by London Underground (not UK Power Network) 
Renewals & 
Incidents associated with upgrade work.  For example upgrade 
Enhancements 
work is completed overnight during engineering hours, but the 
(R&E) 
track is handed back to the operational teams 15 minutes late, 
meaning there is a delay to the start up of services on the line. 
Signals 
Any incident due to some form of signalling issue. 
Stations 
Any incident due to a Stations Infrastructure fault.  This could 
include lifts and escalators being out of service, or a fire alarm 
malfunctioning. 
Track 
Any incident due to some form of track issue – this also includes 
delays caused by track obstructions and vegetation. 
COVID19 
Incidents related to COV19 – examples include lack of operational 
staff due to isolating, looking after others, or deep cleaning of 
equipment/premises.