An exploratory analysis of traffic and collision patterns pre- and post-20mph (32 km/h) implementation in Edinburgh and Glasgow, UK

Journal article

The introduction of 20mph speed limits in urban and residential areas is an increasingly common intervention to mitigate excessive speeds and combat road safety inequalities. In this article, road safety data spanning 12 years (2010–2022) are analysed to examine the potential road safety benefits of newly introduced 20mph zones in Edinburgh and Glasgow, UK. We conduct exploratory and statistical analyses of traffic and road traffic collisions data in Edinburgh and Glasgow to evaluate the effects of the 20mph zones on traffic volumes and various road safety indicators. The findings of the exploratory analysis show that the 20mph schemes likely contributed to reduced car traffic in both case cities. The rate of collisions also reduced in the years following 2016 (i.e., the year the 20mph schemes were introduced); however, the effect on collision severity was more ambiguous. The estimation of collision severity models (binary logit with random parameters and heterogeneity in means) provides further insights into the impact of 20mph speed limits on road safety in the pre- and post-20mph periods, focusing on a collision class that disproportionately affects pedestrians and cyclists: low-speed, single-vehicle collisions. The model estimation results suggest that the post-20mph period was associated with significantly reduced collision severity among single-vehicle, low-speed observations; however, this relationship was not replicated for a pedestrian-involved subset of collisions. The COVID-19 lockdown period was also found to have significant moderating effects on collision severity in the post-20mph period, partially explaining counterintuitive collision severity trends in the post-20mph period.

Authors: Semple, T; Fountas, G

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Frontiers Media
• Journal: Frontiers in Sustainable Cities
• Volume: 8
• Article number: 1801642
• Publication date: 2026-06-15
• Acceptance date: 2026-05-25
• DOI: 10.3389/frsc.2026.1801642
• EISSN: 2624-9634
• ISSN: 2624-9634
• Language: English
• Keywords: pedestrian safety; unobserved heterogeneity; collision frequency; collision severity; 20 mph speed limit; discrete outcome modelling