Parliamentary Advisory Council for Transport Safety (PACTS)
Uploaded to Knowledge Centre
25 May 2023
This research finds that 20mph limits backed by physical measures have substantially greater speed and casualty reduction benefits than those without.
The research project was carried out by the Parliamentary Advisory Council for Transport Safety (PACTS), with together an international team of road safety experts, with funding from The Road Safety Trust.
The project set out to explore the evidence from six countries in mainland Europe as well as in the UK where more and more towns and cities are introducing 20mph limits.
The PACTS report notes that lower urban speeds can play an important role in delivering casualty reductions and increasing active travel.
Indeed, ‘safe speeds’ is one of the five foundations of the Safe System approach to road safety. Safe System aims to manage the magnitude of crash forces so that, in the event of a collision on the road network, no one should be killed or seriously injured. It recognises that people sometimes make mistakes, and that all elements of the road system, for example road design, vehicle construction and user behaviour, contribute to safety outcomes.
The report finds that the extent to which 20mph schemes deliver actual speed and casualty reductions depends on whether they are supported by other measures, such as road humps and/or changes in relative road width.
Schemes without other measures result in modest speed reductions – typically 1-2mph where before speeds are approximately 25mph, and 3-5mph where before speeds are approximately 30mph. When a speed limit of 20mph is introduced with physical measures, speed is normally reduced to less than 20mph, provided it was less than about 30mph before the measures were implemented.
In the UK, signed only schemes result in approximately 11% fewer casualties than before they were introduced.
This figure rises to 40% in schemes where physical measures are introduced, as the speed reduction is substantially greater.
The report also finds that compliance with 20mph limits where no physical measures are in place is poor.
The report notes that Intelligent Speed Assistance (ISA) – which is aimed at increasing compliance with speed limits – is seen as the most effective in-vehicle system for reducing speeding and improving road safety. ISA systems alert the motorist if they exceed the speed limit and encourage compliance. They do not automatically prevent speeding unless the driver selects a mandatory system.
Click the following link to view the full report: