Guidance

Guide to contributory factors (and road safety factors) for reported road casualties Great Britain

Updated 28 November 2024

About this guidance

This guidance relates to the reporting of contributory factors (CFs) within the STATS19 road collision data collection. As a result of recommendations in the 2018 STATS19 review, the collection system is changing to new road safety factors (RSFs). An overview of the new RSFs is provided in our initial analysis.

As most of the data up to end 2023 is recorded as CFs, this guidance focuses largely on those, though it is expected that published statistics will transition to RSFs for the 2024 data year and onwards. The fundamental approach to collection is broadly similar, with the main differences being in the number of factors and how they are grouped, with RSFs being fewer in number and better aligned to safe system pillars.

Overview

Contributory factors

CFs 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 under-reported.

Transition to road safety factors

Following the latest review of the STATS19 collection in 2018, the CFs collection will be replaced with new road safety factors. Further details of the reasons for this change are set out in the STATS19 review reports. Forces will record RSFs rather than CFs as they transition to the new STATS19 specification. For forces using the CRASH system, this was during November 2023 but for some forces will not be until 2025. The above overview broadly applies to RSF collection as well as RSFs.

It is possible to map from the CFs to RSFs, so that data recorded as CFs can be analyses using the RSF categorisation. This has been done for both our initial analysis, which outlines the mapping, and a new factsheet on fatal 4 factors in collisions.

Strengths and weaknesses

Although the following relates to CFs, it will also apply to RSFs in the same way and we will provide equivalent guidance when the recording of RSFs becomes more prevalent. The latest version of the STATS20 guidance covers RSFs.

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 64% of collisions reported to the police in 2023 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 following guidance will also apply to RSF data in the same was as for CF data currently

The contributory factor data are considered sensitive 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 spreadsheet 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.

For road safety factors, there are only 36 factors which are grouped into a smaller number of categories: speed related, roads, vehicles, road user behaviour, impairment or distraction and non-motorised road users.

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

Analysis of CF reporting

The following relates to CFs. Equivalent information for RSFs will be provided when a greater proportion of the data is recorded directly as RSFs.

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	2014	2015	2016	2017	2018	2019	2020	2021	2022	2023
Fatal	93	91	85	87	87	86	84	86	90	89
Fatal or Serious Collisions (unadjusted)	88	86	81	81	81	80	79	80	82	79
Fatal or Serious Collisions (adjusted)	88	86	82	82	81	80	79	80	82	80
All collisions	79	77	73	72	69	67	66	66	67	64

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

Road class	2014	2015	2016	2017	2018	2019	2020	2021	2022	2023
Motorways	88	84	80	81	78	76	75	74	77	73
A Roads	81	80	77	75	73	69	68	68	69	67
B Roads	80	79	74	73	71	69	67	68	69	66
Other roads	75	73	69	67	64	63	62	63	62	60

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

Vehicle type	2014	2015	2016	2017	2018	2019	2020	2021	2022	2023
Pedal cycles	67	65	62	58	55	52	53	52	50	47
Motorcycles	87	86	82	81	80	77	72	71	70	65
Cars	80	78	74	73	70	68	67	68	69	66
Buses or coaches	67	70	68	70	66	64	65	66	69	63
Light goods vehicles	80	78	76	76	73	70	68	68	69	67
Heavy goods vehicles	86	83	79	81	78	77	76	76	79	77
Other or unknown vehicles	78	71	63	62	58	58	62	58	58	55

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

Police force	2014	2015	2016	2017	2018	2019	2020	2021	2022	2023
Avon and Somerset	69	63	67	69	59	58	52	54	58	66
Bedfordshire	71	70	71	69	70	73	65	68	59	53
Cambridgeshire	71	73	71	69	68	66	56	66	57	56
Cheshire	79	80	70	75	75	74	75	70	66	69
City of London	76	74	76	71	73	66	70	53	69	60
Cleveland	75	75	75	80	77	76	73	76	76	68
Cumbria	60	58	63	62	58	72	75	67	68	61
Derbyshire	75	74	73	70	65	64	75	68	69	65
Devon and Cornwall	82	81	77	76	80	81	80	80	79	70
Dorset	73	81	86	80	80	84	77	77	76	73
Durham	73	69	43	27	54	19	18	36	51	47
Essex	80	74	36	36	32	65	60	57	62	61
Gloucestershire	84	86	77	71	58	69	73	76	81	81
Greater Manchester	82	77	60	60	54	48	49	35	32	38
Hampshire	81	81	83	81	80	77	77	74	77	78
Hertfordshire	80	75	70	67	75	75	68	69	61	53
Humberside	75	73	60	57	63	62	64	64	62	60
Kent	82	83	64	54	51	67	71	71	72	70
Lancashire	100	100	100	100	100	76	75	72	74	72
Leicestershire	72	69	73	70	70	73	79	87	94	78
Lincolnshire	84	81	80	81	79	80	84	84	87	81
Merseyside	81	80	81	76	70	70	68	66	64	65
Metropolitan Police	82	83	82	77	71	65	61	60	60	55
Norfolk	85	82	61	76	78	71	45	73	70	65
North Yorkshire	82	82	82	81	80	80	81	74	80	82
Northamptonshire	53	46	52	55	64	70	76	78	76	79
Northumbria	72	71	58	46	34	28	25	30	29	30
Nottinghamshire	74	73	74	74	71	72	73	74	57	51
South Yorkshire	80	81	74	70	73	70	74	72	72	75
Staffordshire	77	46	36	36	34	32	41	54	54	55
Suffolk	86	88	60	73	74	72	46	71	68	59
Surrey	57	56	81	85	83	76	74	73	74	71
Sussex	77	77	75	74	73	73	75	73	74	71
Thames Valley	80	78	81	84	74	68	68	67	66	61
Warwickshire	86	84	77	78	80	75	81	81	79	76
West Mercia	78	79	78	78	78	78	76	79	76	75
West Midlands	74	64	51	45	40	40	51	53	49	44
West Yorkshire	75	73	69	69	69	69	68	73	76	72
Wiltshire	87	76	86	87	88	88	84	84	82	84
Dyfed-Powys	87	81	81	81	80	81	80	76	86	84
Gwent	82	84	82	89	86	88	90	91	84	84
North Wales	79	78	82	83	83	84	83	83	83	81
South Wales	97	97	97	97	95	96	98	94	96	94
Police Scotland	82	84	85	85	86	69	61	76	82	78

Future developments

As noted above, the recent STATS19 review recommended replacing CFs with RSFs.

The majority of published statistics are still based on data recorded as CFs, however this will change for 2024 and 2025 data, by which time the majority of data will be recorded as RSFs and CF data tables will no longer be updated.

As part of the 2023 annual statistics, we have presented data based on both CFs, and separately RSFs (largely by mapping from CF data). For 2024, we do not plan to update the CF tables.

Further details of the proposed transition to RSFs are set out in our initial analysis.

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Contact details

Road safety statistics

Email roadacc.stats@dft.gov.uk