Aligning speeds with road design and human tolerance of crash forces

The Road Safety Foundation has published a new report entitled ‘Determining Safe Speeds’ working with experts in in depth collision investigation research from Loughborough University, TRL, Autoliv and Lösningar. 

The report identifies the speeds that would be required to prevent most deaths and serious injuries. These speeds are evidence-based given the laws of physics and the fragility of the human body. The report does not make recommendations about speed limit setting; it simply reports this evidence-base from in-depth collision investigation studies. 

In this report RSF has established the speeds which would be required to prevent most road deaths and serious injuries on Britain’s roads.  The report does not say that all speeds or speed limits should be set to these speeds, rather that infrastructure needs to be improved or speeds reduced to ensure travelled speeds are better aligned with human tolerances to crash forces.  

Based on the latest publicly available research, the evidence-based maximum operating speeds on British roads if most deaths and life-changing injuries are to be avoided are as follows:

• 10mph where there is a particular prevalence of pedestrians and/or bicyclists and/or motorcyclists, or where there is a heightened vulnerability of pedestrians to impact and injury (e.g. around schools, around hospitals, and in the vicinity of major sports or social/cultural events)
• 20mph in other locations where pedestrians and/or bicyclists and/or motorcyclists mix with cars
• 20mph where cars and HGVs mix and where: head-on collisions are possible (i.e. single carriageways) or side impacts are possible (e.g. at T-junctions and crossroads)
• 30mph where head-on collisions and side impacts are possible only between cars

Higher travelled speeds may be acceptable on roads which have fully segregated facilities for any pedestrians or bicyclists and a physical median between opposing directions of flow (including, for example, no T-junctions or crossroads). On these roads (i.e. some dual carriageways including motorways), the priority is to provide adequate roadside infrastructure measures to ensure that road users are suitably protected if they run-off the road.

Speeds on Britain’s roads are much higher than road infrastructure safely caters for. If the number of road deaths and serious injuries is to be reduced substantially, road authorities therefore need to bring operating speeds down, improve infrastructure provision, or, ideally, both.

What is clear is that the gap between today’s speeds and speeds where most people would not be seriously injured or killed is substantial. If we cannot improve road infrastructure or reduce travelled speeds, we must recognise and reflect on how much risk we are tolerating.