Guidance

Guide to contributory factors for reported road casualties Great Britain

Updated 28 September 2023

Overview of contributory factors

Contributory factors (CFs for short) provide some insight into why and how road collisions occur. They are designed to give the key actions and failures that led directly to the actual impact to aid investigation of how collisions might be prevented.

When police officers attend the scene of a collision, they are able to select up to 6 factors they believe contributed to the collision. These can be assigned to vehicles, casualties or uninjured pedestrians involved. Please note that this does not assign blame for the collision to any specific road user but gives an indication of which factors the attending officer thought contributed to the collision.

The police officer also indicates whether the factor was ‘very likely’ to have contributed to the collision or only have a ‘possible’ link to the collision. More than one factor can be linked to a single road user, and the same factor can be linked to a series of road users.

Officers do not need to carry out a full investigation of the incident before allocating CFs; they usually use professional judgement about what they can see at the scene. Some CFs, such as exceeding the speed limit, may not be obvious to the officer and are therefore likely to be underreported.

Strengths and weaknesses

Please note that not all collisions are included in the contributory factor data. Only collisions where the police attended the scene and reported at least one contributory factor are included. A total of 67% of collisions reported to the police in 2022 met these criteria.

It is also important to note that collisions can have multiple contributory factors attributed to them. As a result, it is advised that you do not add the results of individual factors in our published tables because collisions could be counted multiple times.

The contributory factors are different in nature from the remainder of the STATS19 data which is based on the reporting of factual information. CFs are largely subjective and depend on the skill and experience of the investigating officer to reconstruct the events which led directly to the collision. This should be kept in mind when interpreting the data.

Guidance to police (STATS20) states that the contributory factors reflect the reporting officer’s opinion at the time of reporting and are not necessarily the result of extensive investigation. Furthermore, it is recognised that subsequent enquiries could lead to the reporting officer changing their opinion, for example because something was not obvious at the time or is revealed following a more detailed investigation (such as the driver using a mobile phone, or a hidden vehicle defect).

Factors should be identified on the basis of evidence rather than guesses about what may have happened. This evidence can come from various sources such as witness statements, vehicle and site inspections. It can be of variable quality, which is the reason for recording the assessment of the reliability of the contributory factors.

Data access and confidentiality

The contributory factor data are considered sensensitive as it may be considered that they imply blame and responsibility for a collision. If the factors can be matched with specific collisions (and specific drivers, vehicles or casualties) they may be sub judice to a prosecution, or may lead to individuals or media reports laying accusations at participants in the collision.

As a result, CF data is not made available at detailed record level or in our data download tool. Data are available via our published spreadhsheet data tables, or a data extract can be requested from the road safety team. This is subject to completion of an end user agreement setting out the use of the data and how the sensitive data will be protected.

The department has previously published research looking at appropriate release practices for contributory factors as carried out by the Methodology Advisory Unit at the Office for National Statistics. This outlined the main risks for identifying contributory factors with individuals and what action would be required to take to minimise this risk. In practice, the main change this brought about was allowing the release of a table containing the total number of contributory factors by local authority. This table was published for the first time in 2013 and is now table RAS0706.

Further information and data collection form

The form used by the police to report contributory factors includes a list of 78 contributory factors. These 78 factors fall into nine categories and these are: Road environment contributed, vehicle defects, injudicious action, driver or rider error or reaction, impairment or distraction, behaviour or inexperience, vision affected by external factors, pedestrian only factors (casualty or uninjured) and special codes.

A copy of the form can be found on our STATS19 forms page, as part of the overall STATS19 form. A description of all the CFs used can be found in the STATS20 guidance which can be found at the same link.

Analysis of CF reporting

CF reporting can vary from force to force depending on operational practices, experience of road traffic collisions, systems used and requirements of the force.

Tables 1-4 give more insight about underlying reporting practices.

Table 1: Percentage of reported collisions included in the contributory factor analysis, by severity

Severity	2013	2014	2015	2016	2017	2018	2019	2020	2021	2022
Fatal	92	93	91	85	87	87	86	84	86	90
Fatal or Serious Collisions (unadjusted)	87	88	86	81	81	81	80	79	80	82
Fatal or Serious Collisions (adjusted)	87	88	86	82	82	81	80	78	80	82
All collisions	79	79	77	73	72	69	67	66	66	67

Table 2: Percentage of reported collisions included in the contributory factor analysis, by road class

Road class	2013	2014	2015	2016	2017	2018	2019	2020	2021	2022
Motorways	88	88	84	80	81	78	76	75	74	77
A Roads	80	81	80	77	75	73	69	68	68	69
B Roads	80	80	79	74	73	71	69	67	68	69
Other roads	75	75	73	69	67	64	63	62	63	62

Table 3: Percentage of vehicles in reported collisions directly allocated a contributory factor, by vehicle type

Vehicle type	2013	2014	2015	2016	2017	2018	2019	2020	2021	2022
Pedal cycles	67	67	65	62	58	55	52	53	52	50
Motorcycles	86	87	86	82	81	80	77	72	71	70
Cars	80	80	78	74	73	70	68	67	68	69
Buses or coaches	66	67	70	68	70	66	64	65	66	69
Light goods vehicles	80	80	78	76	76	73	70	68	68	69
Heavy goods vehicles	85	86	83	79	81	78	77	76	76	79
Other or unknown vehicles	76	78	71	63	62	58	58	62	58	58

Table 4: Percentage of reported collisions included in the contributory factor analysis, by police force

Police force	2013	2014	2015	2016	2017	2018	2019	2020	2021	2022
Avon and Somerset	61	69	63	67	69	59	58	52	54	58
Bedfordshire	73	71	70	71	69	70	73	65	68	59
Cambridgeshire	70	71	73	71	69	68	66	56	66	57
Cheshire	77	79	80	70	75	75	74	75	70	66
City of London	82	76	74	76	71	73	66	70	53	69
Cleveland	78	75	75	75	80	77	76	73	76	76
Cumbria	60	60	58	63	62	58	72	75	67	68
Derbyshire	77	75	74	73	70	65	64	75	68	69
Devon and Cornwall	82	82	81	77	76	80	81	80	80	79
Dorset	75	73	81	86	80	80	84	77	77	76
Durham	77	73	69	43	27	54	19	18	36	51
Essex	78	80	74	36	36	32	65	60	57	62
Gloucestershire	87	84	86	77	71	58	69	73	76	81
Greater Manchester	79	82	77	60	60	54	48	49	35	32
Hampshire	82	81	81	83	81	80	77	77	74	77
Hertfordshire	81	80	75	70	67	75	75	68	69	61
Humberside	75	75	73	60	57	63	62	64	64	62
Kent	81	82	83	64	54	51	67	71	71	72
Lancashire	100	100	100	100	100	100	76	75	72	74
Leicestershire	76	72	69	73	70	70	73	79	87	94
Lincolnshire	84	84	81	80	81	79	80	84	84	87
Merseyside	82	81	80	81	76	70	70	68	66	64
Metropolitan Police	82	82	83	82	77	71	65	61	60	60
Norfolk	85	85	82	61	76	78	71	45	73	70
North Yorkshire	84	82	82	82	81	80	80	81	74	80
Northamptonshire	59	53	46	52	55	64	70	76	78	76
Northumbria	72	72	71	58	46	34	28	25	30	29
Nottinghamshire	75	74	73	74	74	71	72	73	74	57
South Yorkshire	77	80	81	74	70	73	70	74	72	72
Staffordshire	75	77	46	36	36	34	32	41	54	54
Suffolk	83	86	88	60	73	74	72	46	71	68
Surrey	64	57	56	81	85	83	76	74	73	74
Sussex	73	77	77	75	74	73	73	75	73	74
Thames Valley	80	80	78	81	84	74	68	68	67	66
Warwickshire	86	86	84	77	78	80	75	81	81	79
West Mercia	79	78	79	78	78	78	78	76	79	76
West Midlands	76	74	64	51	45	40	40	51	53	49
West Yorkshire	64	75	73	69	69	69	69	68	73	76
Wiltshire	85	87	76	86	87	88	88	84	84	82
Dyfed-Powys	87	87	81	81	81	80	81	80	76	86
Gwent	68	82	84	82	89	86	88	90	91	84
North Wales	76	79	78	82	83	83	84	83	83	83
South Wales	96	97	97	97	97	95	96	98	94	96
Police Scotland	84	82	84	85	85	86	69	61	76	82

Future developments

The recent STATS19 review recommended replacing contributory factors with a new category: Road Safety Factors (RSF). The aim of RSF is to ease data collection. RSF intends to provide greater focus by reducing the list of possible factors from 79 to 36, and reorganising them to align to the Safe Systems approach. This information is being collected to create actions that can be used to improve road safety.

The findings of the review recommended that:

• at least one factor should be completed for each participant (vehicle or pedestrian) in a collision
• three to six factors should be recorded overall

It is expected that the new codes will be implemented in 2024.

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Contact details

Road safety statistics

Email roadacc.stats@dft.gov.uk