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Is twenty plenty? - A tale of two UK cities

Researchers have embarked on a major study to evaluate the effects of the recent 20mph speed limit implementation in Edinburgh and Belfast.

Speed limits are introduced (and implemented via signs, lines, and other physical measures) to manage either the maximum or minimum levels of traffic speed for a given road or area. In the UK the first ever maximum speed limit was 10mph! In most cases, speed limits are introduced to set a maximum road traffic speed.

There are many reasons for introducing speed limits; most commonly with the aim of:

• reducing the number of road traffic collisions and casualties
• increasing cycling and walking in a certain area
• helping road users to feel safer (known as liveability).

In many cases, the introduction of speed limits have been met with controversy, with passionate debates for and against. Some people may question whether or not the introduction of a speed limit will achieve the expected goals and whether a speed limit is the most appropriate and effective way of achieving these goals for the area under consideration.

The “Is twenty plenty?” study conducted by the Scottish Collaboration for Public Health Research and Policy, and led by Dr Ruth Jepson, will assess the implementation of the 20mph scheme in both Edinburgh and Belfast. Key outcomes, which are being considered and measured before and after the speed limit implementation, include: The number of road traffic collisions and casualties, the level of cycling and walking, and the perceptions of local residents and drivers. This project draws upon data collected from multiple sources such as the City of Edinburgh household survey, SUSTRANS, Living Streets, and Police data (STATS19 and the Northern Ireland Police Recorded Injury Road Traffic Collision Data). Road users in the implementation areas will also be surveyed on their perceptions of the 20mph speed limit at various points across the course of the project.

Listen and watch our new video where Dr Jepson describes the “Is twenty plenty?“ study in detail.

Interim reports on the latest findings of the project, press releases, and publications can be found on the “Is twenty plenty?” project website. Finally, for further details please contact Dr Jepson at:

The ‘Is twenty plenty?’ study is funded by the National Institute for Health Research (NIHR) and is a partnership between The University of Edinburgh and the Scottish Collaboration for Public Health Research and Policy (SCPHRP) and the Physical Activity for Health Research Centre (PAHRC), in partnership with other UK Universities, NHS Health Scotland, and various charities.

The views and opinions expressed in this blog are those of the authors and do not necessarily reflect those of the NIHR or the Department of Health and Social Care.