The debate over the effectiveness of 20mph speed limits has intensified in recent months, becoming a focal point of media and public discourse. Particularly through Local elections and now through a General Election. With the recent data emerging from Wales, showing a significant reduction in road casualties following the implementation of these lower speed limits, the evidence supporting their efficacy is increasingly compelling.
In the last quarter of 2023, Wales recorded a notable decrease in road casualties on 20mph and 30mph roads, with figures dropping from 681 in 2022 to 463 in 2023. This reduction of a staggering 32% of casualties highlights the potential life-saving impact of lower speed limits. However, setting safer speed limits is only one part of the equation; ensuring compliance is equally crucial. Earlier this year, Agilysis published a report on average speeds across nearly 500km of newly implemented 20mph roads in Wales using connected vehicle data from TomTom in our Traffic Insights reports. Our findings revealed a reduction in average speeds by 2.4mph 3 months after simply changing the posted speed limit.
The success in Wales is part of a broader trend, with cities like Glasgow planning to extend 20mph limits to a majority of their streets. Evidence from Bristol in 2018, evaluated by UWE, demonstrated substantial casualty reductions, translating into significant cost savings. While countless other Cities and Towns are looking to introduce further 20mph limits.
The increasing adoption of Vision Zero and Safe System methodologies underscores a shift towards setting speed limits that prioritize human safety. A safe speed is one at which road users can withstand collisions without severe injury, typically around 20mph for areas with pedestrians and cyclists. At 20mph, pedestrians are far more likely to survive impacts compared to 30mph, where fatality risks increase dramatically. While changing speed limits alone may not suffice, combining them with additional engineering measures can enhance compliance and safety. The PACTS LUSTRE report (May 2023) corroborates this, showing an 11% reduction in casualties across the UK where 20mph limits are present without physical measures, and further reductions still for locations with additional measures.
Human physiology has not changed; our tolerance for impact speeds remains around 20mph. However, our road environments often place vulnerable road users in conflict with faster-moving vehicles. Historically, speed limits have been set based on prevailing speeds rather than safe speeds, creating a mismatch between posted limits, road functions, and engineering standards. International practices are now gravitating towards setting speed limits based on user vulnerability and conflict opportunities, resulting in slower but safer roads.
The recent results out of Wales seem to support our initial prediction that a 3mph reduction in operating speeds could lead to around a 30% decrease in collisions and casualties—a minor change with significant benefits.
Traffic Insights data can help inform evidence-based strategies for safer road environments while offering the ability to evaluate schemes and monitor compliance on a large scale. The positive outcomes observed in Wales and other regions underscore the transformative potential of 20mph speed limits and why they are so beneficial in the presence of vulnerable road users.
