Road casualty statistics: known data issues
Updated 28 November 2024
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This publication is available at https://www.gov.uk/government/publications/reported-road-casualty-statistics-background-quality-report/road-casualty-statistics-known-data-issues
The background quality report for the reported road casualty statistics provides an overview of the statistics, how they are compiled and validated, and an assessment against the different dimensions of statistical quality.
This page provides details of specific known issues affecting the STATS19 dataset which is used to compile the department’s road casualty statistics. Further details are available on request from the road safety statistics team.
Unless otherwise noted, these issues are considered unlikely to noticeably impact on the overall Great Britain road collision trends, but caution should be applied when considering geographical breakdowns by these police force areas (RAS0401) and relevant local authorities (RAS0403) for affected areas.
Known issues affecting several years data
Incompleteness of data for Staffordshire police
Staffordshire police have under-reported collisions in 2023, and for several earlier years, due to issues with timely and completed processing where reportable collisions within their systems were not included in STATS19 returns. Rectifying actions have been discussed with the police force and are currently being implemented to resolve the situation. Provisional data for 2024 suggests that the completeness of the data is beginning to improve.
However, the data for STATS19 is likely to under-count the number of collisions and casualties for Staffordshire relative to other police forces, to a growing degree over time. It is unlikely that this historical issue will be rectified and no attempt has been made to impute for missing data.
In particular, reductions in casualties in Staffordshire from around 2016 are likely to be impacted by completeness of the data reported, as well as any genuine change in road safety in the area. Therefore comparisons between Staffordshire police force or local authority areas and other areas should be interpreted with caution.
2022 known issues
Avon and Somerset police data
Avon and Somerset police changed collision recording systems during 2022. The transition has exposed some formatting and export issues. Most notably key data was missing, which has impacted Local processing authorities (LPA) ability to process and validate the data. This has caused delays in supplying data to the department and as a result some data may be missing or incomplete at time of publication.
Greater Manchester police data
Greater Manchester Police transitioned to a new reporting system in 2021. Minor total differences were reported by Transport for Greater Manchester for 2021 data. Some collisions were not supplied in time for inclusion and some additional deletions were reported alongside the 2022 figures. The overall totals are not significantly different to those published as part of the department’s statistics and STATS19 datasets.
2023 known issues
Speed limit data quality
Ahead of the Welsh Government (WG) Police recorded road collisions: 2023 release, the WG undertook additional validation of the road speed limit data as recorded by police officers at the scene of the collision. This additional validation was undertaken due to the change in the default speed limit from 30mph to 20mph on unrestricted roads in Wales on 17 September 2023 and wanting to ensure that the speed limit data had been correctly recorded.
This highlighted several inconsistences, particularly relating to collisions where the attending police officer had recorded the speed the road where the collision occurred as 30mph, but information provided by local authorities suggested the road was 20mph at the time of the collision. WG have manually corrected the information following confirmation from local authorities in Wales. Further information is available in WG’s Road casualties quality report.
The changes made in Wales but not for Great Britain will impact on the comparability of figures for casualties or collisions by road speed limit. While the speed limit data is considered suitable for high level monitoring, for analysis of specific smaller areas users are encouraged to review what is recorded.