Do 20mph speed limits reduce casualties and increase cycling, walking, and liveability in the general population?

Expert Advisor to Scottish Collaboration for Public Health Research and Policy & Physical Activity for Health Research Centre (PAHRC) along with colleagues from Queen’s University Belfast, University of Oxford, University of Cambridge and Sustrans. NIHR Grant. 20mph speed limits aim to encourage more considerate driving, leading to safer streets for all road users. Lower speeds can reduce the risk and severity of road collisions and related casualties. Reducing traffic speed can also help make people feel more confident about being on their streets on foot or by bike, and may help children and elderly people to travel independently and safely. Calmer roads may encourage people to walk and cycle more which, in turn, contribute to less traffic congestion, better health, less noise, more social interaction and stronger communities. There are a range of different ways of introducing 20mph speed limits including the use of signage, street markings, enforcement, and physical traffic calming measures (such as speed humps). In both Edinburgh and Belfast this relies primarily on laws, signage and road markings. This makes it cheaper to introduce than physical calming methods and also reduces maintenance costs over the long term. The aim of this study is to evaluate the effects of these new 20mph speed limit policies on public health.

Primary outcome measures
Casualty data is taken from STATS19 accident records (collected nationally by the police) at multiple time points pre and post implementation (up to 18 months) of the 20mph zones.
Secondary outcome measures
1. Walking is assessed through automatic fixed pedestrian counters (collected by Sustrans) and using Route User Surveys (collected by Sustrans) at multiple time points before and after (up to 18 months) implementation of the 20mph zones.
2. Cycling is assessed through automatic fixed cycling counters (collected by Sustrans) and using Route User Surveys (collected by Sustrans) at multiple time points before and after (up to 18 months) implementation of the 20mph zones.
3. Public transport use is assessed through routine bus data (collected by the bus companies) at multiple time points pre and post implementation (up to 18 months) of the 20mph zones.
4. Attitudes towards 20mph zones are collected through the Edinburgh Household Survey at baseline and 12 months post implementation of the 20mph zones.
5. Traffic and speed volume is collected through a survey at baseline and 18-months post implementation.
6. Perceptions of public support, behaviour and compliance are collected through a survey at baseline and 18-months post implementation.
7. Liveability is assessed using street audits (by Living Streets) at baseline and 12 baseline and 18-months post implementation.