More than four lives a year have been saved since the introduction of 20mph zones in one of Britain's major cities, a study has found.
Average speeds on roads where the 20mph limit was introduced in Bristol has fallen by a 2.7mph since 2014. Around 11 serious injuries and 159 slight injuries were also prevented - saving £15 million a year, the research by the University of the West of England found.
More than 36 million vehicle movements were analysed by the university team, following the roll-out of 20mph zones in 2014.
Dr Paul Pilkington, the lead author, said: "In January 2014, Bristol began to introduce 20mph speed limits throughout the city, following the completion of successful pilot schemes in south and east Bristol.
"The 20mph speed limit was introduced in six phases, with the process being completed in September 2015.
"The roll-out of the 20mph speed limits in Bristol was about more than reducing road traffic casualties, although this was one of the aims.
"It also sought to improve health and wellbeing across the city, taking a wider perspective as to how slower traffic speeds might impact on people's lives."
Dr Pilkington added: "The reductions in speeds and road traffic casualties are a very promising finding for the city, and for 20mph speed limits in general.
"It offers a model for other towns and cities across the world, who are seeking to reduce traffic speeds, cut road traffic casualties, and promote community health and wellbeing through road danger reduction."