Learning from 25 years of preventative interventions in Scotland

(Part 2: Case Studies) 1. 20 mph Limits

20 mph speed limits in Edinburgh: reducing speeds across the city to improve public health outcomes

In 2016 Edinburgh was the first city in Scotland to introduce 20 mph limits on a citywide basis. The intervention has been robustly evaluated and shown to reduce speed, leading to reductions in collisions and casualties. Public perceptions of safety and compliance with the speed limits also increased. The findings suggest that 20 mph limits can be implemented at scale, lead to positive public health benefits and are likely to be cost-effective.

Introduction

The roll out of 20 mph speed limits in Edinburgh is a primary preventative road safety and public health intervention. The intervention involved the implementation of 20 mph legislation, signage, enforcement, education and awareness-raising. The aims of the intervention were to reduce deaths and casualties, encourage walking and cycling and create a calmer, more pleasant environment. The intervention was designed, implemented and enforced in collaboration with a range of partners from across the public sector. ^[27]

Context

There is a well evidenced relationship between traffic speed and road safety. Both the number of accidents and the severity of accidents increases with speed. ^[28] The 2014 City of Edinburgh Council (CEC) Local Transport Strategy (LTS) sets out evidence that the risk of fatal injury to pedestrians is eight times higher at 30 mph than 20 mph, and the chance of survival halves again between 30 mph and 40 mph. ^[29] Similarly for motorists, the probability of serious injury to a belted front seat car occupant is three times higher at an impact speed of 30 mph than at 20 mph. ^[30]

The main policy goal of 20 mph limits is to reduce road traffic collisions and casualties by slowing down traffic. One of the Scottish Government’s primary visions in the 2009 Road Safety Framework to 2020 was to:

‘…[reduce] the numbers of those killed and those seriously injured, with the ultimate vision of a future where no-one is killed on Scotland’s roads, and the injury rate is much reduced.’ ⁴

Traffic speed was a key component of Vision Zero’,^[31] set out in Edinburgh’s LTS in 2014, which emphasised that vehicle speed is ‘the most important single factor in the severity of road collisions, and urban speeds need to reduce if the Council is to move towards Vision Zero.’³

Scotland’s Road Safety Framework to 2030 (published in 2021) states that ‘the costs of preventing casualties are usually substantially less than the actual costs of treating these casualties.’ ^[32] In 2019 the cost of collisions in Scotland was estimated to be over £1.1billion, highlighting the economic benefits to preventative interventions which reduce the risk of casualties on Scotland’s roads.⁶

Reduced traffic speeds also have wider health and environmental objectives. Lower speeds contribute to ‘place making’ and improving the ‘liveability’^[33] of an area and can encourage walking and cycling and create a calmer, more pleasant environment.^[34] These objectives were also integral to ‘Vision Zero’ in Edinburgh’s LTS.³

There has been a gradual move towards implementing 20 mph speed limits in Scotland over time. The Scottish Government provided almost £50 million funding to local authorities between 2003 and 2008 for the introduction of 20 mph schemes at schools, and by March 2008, 20 mph speed limits were in place at 83% of schools.⁴ In 2009, the Scottish Government encouraged local authorities to implement 20 mph schemes by schools and in residential areas in its Road Safety Framework to 2020.⁴

There is a longstanding road safety inequality due to socio-economic disadvantage, whereby the overall casualty rate in the most deprived 10% Scottish Index of Multiple Deprivation (SIMD) is higher than for the least deprived SIMD.⁶ Scotland’s Road Safety Framework to 2030 states that lower speeds, especially in 20 mph speed zones, reduce the number of casualties, and this is particularly true for disadvantaged areas and communities, and could therefore help to reduce inequalities.⁶

Response

In Edinburgh, discussions about 20 mph speed limits had been happening since around the year 2000, and were subject to public and stakeholder consultations.³

In March 2012, a pilot project of 20 mph speed limits was trialled in south Edinburgh, to assess the viability of relying mainly on signs rather than on physical traffic calming measures (such as speed humps, chicanes, road narrowing etc.) ^[35] The results of the trial were positive, with 79% of the 1,000 people surveyed in the pilot area supportive of the new speed limit and 4% opposed to it. This pilot was critical in gaining widespread public support for the wider roll-out in Edinburgh. ^[36]

In June 2014, Edinburgh residents were consulted on extending the pilot to a citywide scheme. The majority of the respondents were in favour and in January 2015 a public consultation was held to determine which roads to include.⁹ The consultation highlighted some opposition and concern from bus operators and taxi drivers about the impact of 20 mph limits on their operations and journey times, as well as concerns over enforcement of 20 mph limits. The City of Edinburgh Council pledged to work with bus operators and road safety partners to resolve these issues.³

Intervention

The intervention involved the implementation of 20 mph legislation, signage, enforcement and education and awareness-raising across all streets that fell within the CEC ‘citywide’ area. This is distinct from 20 mph zones which include traffic-calming measures like speed bumps.

The 20 mph network was implemented under one citywide speed limit order, approved in January 2016 which allowed works to start.⁹ Twenty mph limits became law and enforceable on 31 July 2016, and the roll out began in July 2016 and was complete by March 2018.¹⁰ Prior to the intervention, half of Edinburgh’s streets already had 20 mph speed limits but the intervention increased this, and the city was split into seven implementation zones, implemented over phases. Each phase lasted around 16 weeks, over a period of 24 months.¹⁰

Source: City of Edinburgh Council Transport and Environment Committee (2019) Evaluation of the 20mph Speed Limit Roll Out

The cost of the scheme in Edinburgh was £2.81 million,^[37] and it was jointly funded by the CEC’s Transport Capital Budget, the Scottish Government and SUSTRANS.¹⁰

Over 29 public sector stakeholder groups were involved in the implementation, decision-making and evaluation processes, including: the council, charitable organisations (Sustrans, Living Streets), public transport companies (bus and taxi), driver groups, the local health board, Transport Scotland, the Scottish Fire and Rescue Service and 159 members of the general public.^10,1

Twenty mph speed limit interventions had been introduced in other UK cities and were expected to result in both lower traffic speeds and fewer casualties, and an improvement in the perception of safety and a subsequent increase in active travel. However, there was a limited evidence base on the effectiveness of 20 mph speed limits prior to the intervention in Edinburgh, and improving this was a key reason for the evaluation.

Monitoring and Evaluation

An independent evaluation of the public health impacts of the introduction of 20 mph limits in (a comparative study of) Edinburgh and Belfast was conducted by the Scottish Collaboration for Public Health Research and Policy (SCPHRP). The evaluation involved researchers from a number of Universities as well as partners from Public Health Scotland and SUSTRANS.

The evaluation was funded by the National Institute for Health and Care Research (NIHR), and the funding ran from March 2017 until August 2020. A lengthy study allowed data to be collected a year after the implementation of the 20 mph limits in Edinburgh. Driver behaviour can take time to change and stabilise so this enabled sufficient time to have passed to ascertain whether the behavioural changes were temporary or more enduring.¹⁰

The evaluation was a robust mixed-methods study that included a process, impact, policy and economic evaluation of two natural experiments.¹⁰ These comprised before-and-after (controlled when possible) studies in Edinburgh and Belfast, using matched geographic control zones whenever possible. Twenty mph limits had been introduced in Belfast city centre (in contrast to citywide) from 2000 to 2018. When the study results were published in 2022, this was the most extensive evaluation of 20 mph limits in the UK.¹⁰

The objective was to evaluate and understand the processes and effects of developing and implementing 20 mph speed limits in both cities. The evaluation examined:

(1) the political decision-making that led to the schemes;

(2) how the schemes were delivered (the ‘how’ and ‘what’ of implementation);

(3) the impact of the schemes on speed, collisions and casualties, perceptions of the safety and pleasantness of people’s home and work environments, and impact on active travel;

(4) whether or not the schemes were a sensible financial investment.

The main outcomes measured were; speed, type and severity of road collisions, public perceptions of safety, mode of travel, driver behaviour and attitudes, and liveability.

There were some limitations. For example, the data did not allow for an analysis of: active travel outcomes; the impact on health inequalities; and an economic evaluation.¹⁰

Key Findings

The evaluation found that the citywide implementation of 20 mph limits was effective at reducing speed in Edinburgh, leading to reductions in collisions and casualties. It found that 20 mph limits can lead to similar public health outcomes as 20 mph zones, and have the advantage of being less costly and less intrusive. However, to be most effective they may need to be implemented at a citywide level, or in areas where speeds are high, and be combined with significant education and awareness-raising.¹⁰

‘These findings suggest that 20 mph limits can be implemented at scale, lead to positive public health benefits and are likely to be a sensible financial investment.’ ¹⁰

a) Reductions in speed

The speed data used in the analysis covered 66 streets where the speed limit was reduced from 30 mph to 20 mph as part of the roll out. Mean speeds reduced by 1.34 -mph (from 23.63 mph ‘before’ to 22.29 mph ‘after’), at 12 months. Figure 1 below shows how the number of vehicles with average speeds of 20 mph or less increased following the rollout.

Source: City of Edinburgh Council Transport and Environment Committee (2019) Evaluation of the 20mph Speed Limit Roll Out

b) Reductions in collisions and casualties

The overall percentage reduction in casualty rates was 39%, and in collision rates was 40%. The percentage reduction for each level of severity was 23% for fatal casualties, 33% for serious casualties and 37% for minor casualties.

c) Cost savings

It was not possible to produce a full economic evaluation, however, the interim economic evaluation suggested that it is likely that the benefits of the 20 mph limits in Edinburgh, associated with the reduction in collisions and casualties, would exceed the costs. There was a small increase in liveability, and these observed increases strengthen this conclusion.¹⁰

Separate analysis by the CEC in 2022 applied Department for Transport estimates of the monetary value that can be attached to types of road traffic collision involving personal injury (fatal, serious and slight), at 2020 prices. It found the total monetary saving as a result of the reduction in collisions in Edinburgh since implementation of the 20 mph limits, equates to £38,582,514.^[39]

d) Public perceptions

There was an increase in support for 20 mph and rule-following after implementation which was supported by the qualitative data.

e) Implementation

The Edinburgh scheme was broadly implemented as intended in terms of signage, education and enforcement. The pre-implementation phase and pilot schemes were found to be important in gaining public support, and framing political attitudes.

The evaluation found that important factors in the implementation of the scheme (in both cities) included local histories, the political context, local policy goals, local priorities and strong leadership, (individual politicians were pivotal in progressing the 20 mph limits).¹⁰ Opposition parties did not provide strong opposition to the intervention and community councils were actively supportive, and considered critical in giving the politicians sufficient ‘weight’ to drive the initiative forward.¹⁰

A dedicated ‘20 mph team’ within CEC was created to help navigate challenges in the roll-out of the intervention. The report wrote: ‘the creation of a dedicated official, and strong partnership and joined-up working, were identified as key facilitators of broad implementation and the delivery of a tailored education and awareness-raising campaign in Edinburgh’.¹⁰

Learning and Next Steps

Recent evidence from Wales further demonstrates the impact of 20 mph speed limits on reducing accidents and improving community safety. The latest police recorded collision statistics from Wales (from January 2025), covering the period of July to September 2024, provide the first year of statistics since the default 20mph speed limit was introduced. These show collisions on Welsh roads at their lowest level for that quarter since records began.^[40]

Scotland’s Road Safety Framework to 2030 commits to giving all appropriate roads in built up areas a speed limit of 20 mph by the end of 2025.^6,[41] The roll out is intended not only to enhance road safety but also to encourage more walking and cycling, supporting healthier, more sustainable travel choices.^[42],[43]

This was a complex intervention involving many partners, and collaboration was instrumental to the successful delivery of the rollout of this policy. A 20 mph task group has been exploring the most effective way of achieving that commitment in Scotland, and in December 2023 it was agreed to support local authorities to expand 20 mph speed limits where appropriate as the optimum route to implement.

The Scottish Government published guidance and provided £4 million of funding in 2024-25 to local authorities to enable them to deliver this. This is supported by a comprehensive Implementation Guidance to ensure consistency and effectiveness across Scotland.