A study by the London School of Hygiene and Tropical Medicine suggests that 20mph speed zones have cut road injuries by more than 40% in London.
In particular the number of children killed or seriously injured has been halved over a 15-year period.
The study estimates 20mph zones have the potential to prevent up to 700 casualties in London alone and as a result concludes that UK cities should have more 20mph zones.
Dr Chris Grundy, a lecturer at the London School of Hygiene and Tropical Medicine, said: "This evidence supports the rationale for 20mph zones, not just in major cities in Britain, but also in similar metropolitan areas elsewhere.
"Indeed, even within London, there is a case for extending the currently limited provision of such zones to other high casualty roads."
A spokesman for the DfT said the study backed their own research: "Our road safety strategy consultation recommends that local authorities introduce, over time, 20mph zones or limits into streets around schools, and which are primarily residential in nature, to protect pedestrians and cyclists.
"This will save lives and make people feel more secure in walking and cycling on those streets."
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