20mph speed limits cut road deaths and injuries, according to the British Medical Journal (BMJ).
The BMJ found that road casualties were slashed by 42% in London where 20mph zones had been introduced.
The publication also found that causalities fell by around 8% on roads close to the 20mph zones.
Greatest reduction among the young
The BMJ's report said that the greatest reduction in deaths and injuries was in young children.
Road safety charity Brake said: 'This report, and the emerging evidence from implementation of 20mph limits across many streets demonstrate very clearly that dropping speed limits is a major life-saver.
'The Government should urgently release planned guidance to local authorities to implement 20mph limits in communities, and Brake urges all drivers to pledge now to drive at 20mph in areas around homes, schools and shops, whether the limit is 20 or 30.'