Title: Is 20 plenty for health? Evaluation of the 20mph speed limit networks in Edinburgh and Belfast on a range of public health outcomes
Funder: Chief Scientist Office, Scotland

Abstract: Background: Transport initiatives such as reduction of speed limits to 20mph are expected to result in fewer casualties and lower traffic volumes, leading to an improvement in the perception of safety and a subsequent increase in cycling and walking. Lower speeds may also lead to more pleasant environments to live, work and play in. The main research question is: what is the impact of city-wide 20mph legislation on road casualties and numbers of people walking and cycling? Additional research questions focus on perceptions of safety and; how and why impact does or does not occur; and what can be learnt from implementation in Belfast, Edinburgh and other UK cities? Intervention: Introduction of 20mph legislation, signage, enforcement and publicity in Edinburgh and Belfast, funded by local government and Sustrans. It was implemented in Belfast in early 2016. In Edinburgh it is being phased in over a two year period, starting in July 2016. Both cities have committed funds and resources for implementation and some local evaluation. This provides a rare and exciting opportunity for a wide-ranging evaluation. Population: whole population of each city Design: mixed methods, quasi-experimental study that will comprise an impact, process and policy evaluation. We will use a wide range of data sources (including routinely available, policy documents, surveys and qualitative data). Evaluating the scheme in both cities will help ensure generalisabilty of findings. Outcomes: 1) Total number of road casualties using routinely collected data from the police 2) Number of journeys made by foot and by bicycle using surveys and counters 3) Public perceptions of safety, mode of travel, driver behaviour and attitudes using surveys 4) Perceptions of community using street audits and surveys Length of follow-up: 1-3 years post-implementation (depending on timing of the phases) Duration: 3.5 years (Jan 2017- June 2020). Edinburgh implementation will not be completed until early 2018, so some one year follow-up data will not be available until 2019. In preparation we have undertaken qualitative work to develop a programme theory. In addition (and complementary) to the impact evaluation, we will undertake an in-depth evaluation to understand the implementation process and explore the causal mechanisms and pathways (whether the programme theory works as intended). This will involve interviewing key stakeholders and informants and undertaking 20 focus groups in Edinburgh and Belfast. We will interview groups who may be differentially affected by the intervention to explore their perceptions and experiences (e.g. older people, parents, people with mobility difficulties; shift workers, and people from economically and socially disadvantaged backgrounds). We will use the qualitative findings to provide a nuanced and rich understanding of the quantitative findings. Given that most public health interventions are implemented in complex systems, we will also explore and explain the political, policy and cultural agendas that led to implementation in both sites and more widely in the UK. As both Northern Ireland and Scotland have legislative powers for transport, we will explore the process in English sites to provide useful learning across jurisdictions and help inform transferability UK wide and development of implementation guidance. Finally, we will perform economic modelling if the intervention results in the expected changes.

Lay abstract: This study aims to evaluate the public health impact of a 20mph city-wide speed limit intervention in urban areas of Edinburgh and Belfast. 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, contributes to less traffic congestion, better health, less noise, more social interaction and stronger communities. Thus an intervention that targets motorists may have positive outcomes for the whole community. There are a range of different approaches to 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 the interventions rely primarily on legislation, signage and road markings. This makes it cheaper to introduce than physical calming methods and also reduces maintenance costs over the longer term. Implementation in Edinburgh is taking place in six areas of the city over a two-year period (four different time points) beginning in July 2016. Belfast is implementing the 20mph limit at a single time point (early 2016), which will provide a useful contrast. In this study we will focus on the effects on the following outcomes: - road casualties - walking, cycling - perceptions of safety - driver behaviour and attitudes - how pleasant the local area is to live and work in The aim of the proposed evaluation is to establish whether these new 20mph speed limit policies are successful in achieving the desired outcomes outlined above. We are interested not only in the effects of the intervention on the number of road casualties, but also on the number of journeys made by bicycle and on foot. We will research all stages of the intervention from pre-intervention (how and why was it seen as a priority?) to post-intervention (is it enforced and do people reduce their speed?). We also wish to establish how effectiveness differs according to characteristics of the population (for example, people who live in areas of social disadvantage, the elderly, ethnic minorities). It could be that some benefit from having speeds reduced, but others might be disadvantaged, or have no benefit at all. We propose a study design that enables us to look at the intervention from ‘all angles’ so that we can learn as much as possible about the pre-implementation, implementation and post-implementation process and outcomes. Taking such a broad focus will generate a wealth of evidence and learning that will be invaluable for informing future roll-out of such interventions in other areas of the UK and around the world. We will also be looking at documents and reports from other cities in the UK to gain more understanding. Finally we will be evaluating whether it is value for money (if is shown to be effective).

Research activity codes: 3.1 PRIMARY PREVENTION INTERVENTIONS TO MODIFY BEHAVIOURS OR PROMOTE WELL-BEING
Health categories: INJURIES AND ACCIDENTS