Road safety factors (previously contributory factors)

Background: The collection of contributory factor and road safety factor data

Contributory factors (CFs) were first included as part of the stats19 data collection in 2005. From that point, police officers attending the scene of a collision were able to select up to 6 factors that they believe contributed to the collision from a set of 77. These could be assigned to vehicles, casualties or uninjured pedestrians involved.

Contributory factors were developed to provide insight into why and how road collisions occur. Their aim was to help identify the key actions and failures that led directly to the actual impact, to aid investigation of how it might have been prevented.

As a result of the most recent stats19 review, these contributory factors were replaced by a reduced, revised set of factors known as road safety factors (RSFs). The general principles and aims remain the same as with contributory factors.

From the end of 2023, Police Scotland have been transitioning to the updated approach. According to the current stats19 specification a reporting office attending the scene of a road collision may select up to 6 road safety factors (from a list of 35) to assign to that collision. Multiple factors may be listed against any participant or vehicles in the collision.

Each factor falls under one of 6 categories:

• Behaviour or inexperience
• Distraction or impairment
  Non-motorised road users or PPT (pedestrian, cyclist, horse rider or powered personal transporter)
• Road
• Speed related 
• Vehicles

This transition has been gradual. Over the course of 2024, Police Scotland recorded details for around half of collisions using CFs and around half of collisions using RSFs.

Comparability between road safety factors and contributory factors

In some cases, the new RSFs are a direct equivalent of an existing CF (for example, R2 ‘road surface slippery due to weather’ is a direct equivalent of CF 103). In other cases, several CFs have been combined into one RSF, for example where there is little analytical benefit in having separate factors to ease the burden on reporting police officers. For example, CFs 405 (driver or rider failed to look properly) and 406 (driver or rider failed to judge other person’s path or speed) have been grouped together in B4 (ineffective observation).

This means that there is a ‘many to one’ mapping between CFs and RSFs and it is possible to recode CFs as RSFs (with some limitations). The system used by Police Scotland for recording data on injury collisions now does this recoding automatically before the data is exported to Transport Scotland. Further information on the mapping between CFs and RSFs can be found on the Department for Transport’s website.

However, despite the ability to recode CFs as RSFs, GB-level analysis by the Department for Transport has highlighted that there are differences between data recorded directly as RSFs and data that has been recoded to RSFs from CFs. This analysis found:

• For collisions where RSFs were recorded directly, a higher number of RSFs were recorded per collision than those intially recorded using CFs then recoded.
• The move to directly collecting RSFs results in a change in which factors are being recorded.

This led to the conclusion that there is an apparent step change in the factors that are being recorded by police forces as a result of the move to directly collecting RSFs.

Approach within this publication to road safety factor data

Given the step change between data recorded directly as RSFs and data that has been recoded to RSFs from CFs, this publication does not combine the two types of RSF data. This publication presents findings only for collisions where data was directly recorded as RSFs. This means that figures within this section and the accompanying tables relate to around half of the recorded injury collisions in 2024. Table N, which previously provided limited time series comparisons of contributory factors, has not been updated.

This is the first edition of this publication which presents findings for RSFs. For future editions, we will continue to keep how we present RSF data under review.

Both the 2024 CF and 2024 recoded RSF data can be requested via transtat@transport.gov.scot.

Findings

Tables M to T present road safety factor findings for 2024, including breakdowns for different collision and casualty severities, and different road users. These findings relate only to collisions where RSFs were recorded directly.

Figure 11 shows the proportion of injury collisions with at least one RSF recorded that fall into each RSF category. A collision can be assigned multiple factors and therefore the numbers in Figure may sum to more than 100%. The 3 categories with the largest number of collisions were:

• Distraction or impairment
• Speed behaviour
• Behaviour or inexperience

In terms of individual RSFs, the ten RSFs which were recorded for the highest proportion of injury collisions are shown in figure 12. The RSF recorded in the highest proportion of collisions was ‘Ineffective observation by either the driver, rider or pedestrian’, which was recorded for over half of injury collisions (58%) where RSFs were assigned.

General guidance on the interpretation of road safety factors

Guidance on recording road collisions is provided in the Department for Transport’s Stats20 document which includes the following points on RSFs:

• RSFs reflect the reporting officer’s opinion at the time of reporting, and may not be the result of extensive investigation;
• subsequent enquiries could result in a change in the reporting officer’s opinion;
• the RSFs are largely subjective, and depend upon the skill and experience of the investigating officer to reconstruct the events which led directly to the collision;
• the need to exercise judgement when recording RSFs is unavoidable;
• RSFs should be identified on the basis of evidence from sources such as witness statements and vehicle and site inspections;
• the evidence may be of variable quality, so the officer should record very likely or possible for each RSFs;
• when there is conflicting evidence (e.g. conflicting witness statements), the reporting officer should decide on the most credible account of the collision and base the codes on this, taking into account all other available evidence.

Regardless of the number of vehicles involved in the collision, at most six sets of RSFs data can be recorded per collision. Each set contains three pieces of information:

• a factor which is thought to have contributed to the occurrence of the collision – selected from list of 35 , such as:
  • exceeding speed limit (RSF code S1);
  • travelling too fast for the conditions (S2);
  • Ineffective observation by driver/rider, cyclist, pedestrian, equestrian (B4);
  • Affected by alcohol (D1);
  • Affected by drugs (D2)
• the participant in the collision to whom the factor is related:
  • whether this is a:
    • Vehicle – in which case the factor may relate to the driver/rider or to the road environment;
    • Casualty – a pedestrian or a passenger in a vehicle; or
    • Uninjured pedestrian.
  • if a Vehicle or a Casualty, the relevant Stats 19 reference
• whether it was thought ‘very likely’ or just ‘possible’ this factor contributed to the occurrence of the collision

Therefore more than one factor may be recorded for the same participant and any given factor may be recorded for two or more different participants, subject to the limit of a maximum of six sets of RSF data per collision.

More detailed information is available in the DfT’s Stats 20 document and the procedure for allocating them – for example:

• the RSFs may be recorded in any order (so nothing can be inferred from the order in which they appear);
• more than one RSF may be related to the same road user; and
• the same RSF may be related to more than one road user.

Worked example

Clearly, there could be a lot of RSF information in the case of an collision which involved several vehicles, if it was thought that several of them contributed to its occurrence. The following is an example of the potential complexity of the RSF data. Car 1 is rapidly travelling along a straight road when Car 2 suddenly appears in front of it, having emerged from a pub car park. The driver of Car 1 brakes sharply, to avoid a collision. As Car 2 drives off, Car 1 is hit from behind by a motorcycle, whose rider and passenger are both killed. The following might be recorded as the RSFs data for this collision:

CF no. Participant Contributory Factor How likely? 1 Car 1 Exceeding speed limit Possible 2 Car 2 Affected by alcohol Possible 3 Car 2 Ineffective observation by driver/rider, cyclist, pedestrian, equestrian Very likely 4 Car 1 Driving too slowly for conditions Very likely 5 Motorcycle Passing too close to cyclist, horse or pedestrian Very likely 6 Motorcycle Exceeding speed limit Possible

This collision has three participants and six RSFs, two of which are the same (exceeding speed limit) but apply to different participants (Car 1 and Motorcycle), (therefore percentages in the tables provided may not sum to 100).

Care should always be taken when interpreting the factors as they:

• reflect the reporting officer’s opinion at the time of reporting the collision (or the opinion of a person whose duties include deciding which factors should be recorded based on the officer’s report).
• are based on the information which was available at that time, so may not be the result of subsequent extensive investigation (indeed, subsequent enquiries could result in the reporting officer opinion changing).

Because of this, analysis of road safety factor information requires careful consideration; figures will differ depending on the focus of the analysis. Care should be taken when interpreting tables provided here which consider different aspects of the data (i.e. collisions, vehicles/participants, casualties and frequencies).

Note that most tables are by individual road safety factor so care needs to be taken when carrying out analysis. Adding together numbers for individual contributory factors will result in some double counting e.g. some collisions will have 'exceeding speed limit' and 'driving too fast for the conditions' recorded as a factor.