20’s Plenty

The 20mph revolution

The UK’s Road Safety Foundation (RSF), which carries out research on road safety, advocates for 20mph urban speed limits as the most critical solution. There is plenty of data in support of the speed reductions. For example, Transport for London’s recent analysis showed a 20mph speed limit on key London roads has led to a 25% reduction in collisions and serious injuries. A study of Spanish urban roads following a speed reduction to 30km/h (18.6 mph) and showed the same 25% fall in fatalities, amounting to 97 fewer deaths for vulnerable road users.

There are survivability curves showing the risk of being fatally injured rockets upwards beyond 20mph. The upshot is that under the safe system, we should be either managing vehicle speeds under 20mph where people are walking and cycling or providing segregated facilities to enable them to walk and cycle away from danger.

A lot of progress has been made in making 20mph zones more common. For example, 18 million people in England lived in areas with 20mph limits (most of the largest urban areas).

Complete English counties, such as Lancashire and Cornwall, have introduced 20mph as a default in urban centers. Meanwhile, Scotland is looking to set 20mph as it’s norm in towns by 2025 and Wales will make it mandatory within its towns and cities by this year. In many European countries 30km/h has been mandated in busy urban areas.

Mandating 20mph is the most effective and cost-effective strategy. It’s not the silver bullet, but it’s the best thing you can do that is population wide. Most approaches to road safety are site-specific. Planners notice there are lots of crashes at a junction, so they redevelop it. It’s concrete-led and suffers from the law of diminishing returns. You’ve got to put more and more concrete down to solve those issues.

There is evidence that site-specific calming measures can have some negative impacts. They remind drivers they should revert to normal once they are beyond the site. When there is physical calming outside schools, drivers often speed up as soon as they are beyond it. But children need to be safe all along their journey to school. That’s why we advocate population wide changes to speed limits.

And introducing 20mph speed limits is far more cost-effective than re-engineering infrastructure. You can put speed bumps down a street, and it will affect 250 people. It slows traffic down by 10mph. But fore the same cost, you can put a 20mph limit across a whole community and reach thousands of people.