The Impact of 20mph Speed Limits

23 April 2025

A new research briefing from the Parliamentary Office of Science and Technology (POST) provides a comprehensive overview of how 20mph speed interventions are affecting road safety, public health, and health equity across the UK.

The review offers strong evidence that 20mph zones—particularly those supported by physical measures—consistently reduce traffic collisions and casualties. By contrast, 20mph limits based on signage alone are less reliable without enforcement or supporting design changes.

Importantly, it emphasises that successful interventions should be multi-component—combining infrastructure changes, communication, and enforcement. This aligns with the Safe System principle which recognises that safety is achieved with a collective effort.