Vehicle speed monitoring data: September 2023 to February 2024

Vehicle speed monitoring data: September 2023 to February 2024

This release summarises the vehicle speed data from selected monitoring sites across Wales. All roads monitored had a 30mph speed limit before 17 September 2023 and a 20mph speed limit from 17 September 2023 onwards. At the time of monitoring, all roads were largely free from physical restrictions or obstructions that reduce traffic speeds.

This data supersedes the preliminary data (20 February 2024).

The analysis is based on a total of eight weeks of speed monitoring, with four weeks pre-implementation (before 17 September 2023) and four weeks post-implementation (after 17 September 2023).

The pre-implementation monitoring took place over two, two-week periods in July and September 2023. Post-implementation speed monitoring occurred over a two-week period in November 2023 and two weeks in January 2024.

Summary

The data in this publication will be used to monitor progress against the following three Key Performance Indicators (KPIs), outlined in the national 20mph monitoring framework (September 2023).

Percentage traffic compliance with the 20mph speed limit (KPI 1.1)

For the purpose of KPI 1.1, anyone driving at or below 24mph is categorised as compliant with the new speed limit. Across all monitoring areas and sites, 57.8% of vehicles were travelling at or below 24mph following the introduction of the default 20mph speed limit on restricted roads. Before the introduction, 20.2% of vehicles were travelling at or below 24mph. 

Change in 85th percentile speed (KPI 1.2)

The 85th percentile speed, weighted by total vehicle volume, has decreased by 3.9mph, from 33.1mph to 29.2mph.

Change in the mean speed (KPI 1.3).

The mean speed, weighted by total vehicle volume, decreased from 28.9mph pre-implementation to 24.6mph post-implementation, a reduction of 4.3mph.

Vehicle speed distribution

Overall speeds have decreased. The proportion of vehicles recorded travelling at 15-19mph increased from 3.5% pre-implementation to 16.4% post-implementation. Similarly, the share of vehicles travelling between 20-24mph has increased by 23.6 percentage points to 38.9% post-implementation. The number of vehicles recorded travelling at 25-29mph, 30-34mph and 35mph and above have all reduced following the introduction of the default 20mph speed limit.