New: measuring the impact of a 20mph speed limit on road casualties in Scotland

Our new report estimates the impact of a 20mph speed limit on road casualties in Scotland and the associated monetary value of prevention, adapted from a modelling approach used previously in Wales.

Three different potential scenarios are presented based on speed reductions observed in previous 20mph limit schemes and the resulting anticipated casualty reductions. The three scenarios are: a higher estimate of a 13.5% reduction in casualties – based on average speed reductions seen in a permanent 20mph limit scheme in Bristol; a middle estimate of 9.5% – based on average speed reductions observed in a 20mph pilot scheme in South Central Edinburgh; and a lower estimate of 2.6%, to show the reduction in overall casualties needed to save just one life. The estimated reduction in casualties and associated monetary values of prevention under each scenario were:

• Scenario 1 (13.5% reduction in casualties) 755 fewer casualties, including five fewer fatalities, associated with savings of £39.9 million per year
• Scenario 2 (9.5% reduction in casualties) 531 fewer casualties, including three fewer fatalities and a saving of £27.1 million per year
• Scenario 3 (2.6% reduction in casualties) 145 fewer casualties, including one less fatality and a saving of £7.8 million per year

The paper makes clear that the success of introducing a 20mph speed limit on urban roads in Scotland would be impacted by different local contexts and the effectiveness of complementary activities in advance of and during implementation, such as communication and behaviour change campaigns and supportive policing and enforcement.

The report was developed in response to a request to provide evidence in relation to the forthcoming Scottish Parliament Member’s Bill proposing the introduction of a 20mph limit in urban settings across Scotland.

Bruce Whyte, Public Health Programme Manager at the GCPH and author of the report said:

Reducing road traffic speed in our towns and cities will save lives and reduce the number of people injured on our roads, particularly among more vulnerable road users like pedestrians and cyclists. Lowering the average road speed will make roads safer and help to encourage more people to walk and cycle, contributing to greater physical activity, better air quality and reduced carbon emissions. 

A safer lower speed environment around schools would also encourage more children to walk, cycle and scoot to school and would help to embed every day active travel at any early age.

Access the full report

The report was covered in The Herald and Bruce Whyte also appeared on BBC Radio Scotland to talk about the study.