Why are more towns and cities moving to 20mph?

Supporters say the evidence increasingly points to safety benefits.

Research by the University of the West of England found average speeds fell by 2.7mph after 20mph limits were introduced in Bristol, while the Welsh government also reported reductions in vehicle speeds following its rollout.

Campaigners argue lower speeds not only reduce the likelihood of collisions but also make any crashes that do happen less severe.

Sue Nicholls, director of the charity 20’s Plenty For Us, said lower speed limits could bring wider benefits, including reduced traffic noise, improved air quality and safer conditions for walking and cycling.

Prof Panos Georgakis, an expert in intelligent transport systems at the University of Wolverhampton, said the physics behind lower-speed collisions was clear.

“A vehicle travelling at 30mph has just over twice the amount of kinetic energy as one travelling at 20mph, so the force that will hit an individual is double,” he said.

“If an accident takes place, the injuries will be much more serious, especially for vulnerable people such as the elderly or young children.”