Question to the Department for Transport:

To ask the Secretary of State for Transport, what assessment he has made of the potential effect of a reduction in speed limits outside schools from 30 mph to 20 mph on the level of road traffic incidents.

In November 2018, the Department for Transport published an evaluation into 20mph limits (which are marked by signs only): https://www.gov.uk/government/publications/20-mph-speed-limits-on-roads.

The study found insufficient evidence to conclude that in residential areas the introduction of 20mph limits had led to a significant change in collisions and casualties. However, one city centre case study did show a significant reduction in collisions and casualties.

Overall the introduction of 20mph limits led to a small reduction in median speed (less than 1mph), but vehicles travelling at higher speeds before the change of speed limit reduced their speed more than those already travelling at lower speeds.

Research in 1996 showed that 20mph zones (which have traffic calming) could reduce the overall average annual collision frequency by up to two-thirds.