20 mph speed limits and zones: public health impacts

DOI: https://doi.org/10.58248/PB65

• Policies to limit vehicle speeds to 20 mph are widespread in England, the UK and Europe. These policies aim to improve road safety, including through reducing road traffic collisions.
• There is strong evidence that 20 mph limits and zones are associated with reduced road casualties and fatalities. After Wales introduced a default national speed limit of 20 mph on restricted roads, casualties on 20 mph and 30 mph roads in Wales declined by 24% in April to June 2024 compared to the same period in 2023 (before the national default 20 mph speed limit was introduced).
• Introducing 20 mph limits and zones may have wider benefits to physical and mental health, including encouraging active travel (such as walking and cycling), improving air quality and reducing noise pollution. However, very few evaluations measure health outcomes directly, which can make it difficult to attribute health benefits directly to the introduction of 20 mph interventions.
• Many studies are observational, where researchers compare outcomes before and after a 20 mph speed limit is introduced. Confounding factors make it difficult to compare across studies, including traffic volume, pedestrian activity, and additional road safety interventions. Researchers may also compare data at different points in time, meaning observed differences could reflect short-term fluctuations and/or long-term effects.
• There is strong evidence for a relationship between road traffic and health inequalities. For example, people who live the most deprived areas are at greater risk of being killed or injured on the roads than people in less deprived areas. However, analyses from multiple studies have concluded that more evidence is needed to establish whether 20 mph interventions can reduce health inequalities.
• The potential health benefits of 20 mph zones and limits depend on drivers complying with the speed limit. Measures to promote compliance include changes to the physical environment (such as road signs), wide-spread implementation of 20 mph limits to provide consistency across roads, public engagement and educational campaigns and enforcement.