Lower speeds would improve traffic flow, the report found
The speed limit on hundreds of roads in London should be reduced to 20mph, according to a London Assembly report.
The report highlighted a Transport for London study which found 880 residential roads across the city would benefit from the lower limit.
Slower cars would cut casualties by 42% and lower emissions, the report found.
Currently 400 roads in London have a 20mph limit and eight boroughs are working towards introducing the same restriction on all residential roads.
Lower speeds would also improve traffic flow and could encourage residents to walk and cycle, the report said.
The boroughs of Islington, Hackney, Southwark, Brent, Kingston-upon-Thames, Lambeth and Tower Hamlets are working to introduce borough-wide 20mph speed limits.
Islington Council, which has the lower speed limit on a number of roads, aims to impose a 20mph limit on all residential roads by March 2010.
A further six boroughs are also looking to introduce a default 20mph limit, but plan to go ahead only after monitoring the effectiveness of the scheme in the eight areas, the committee said.
The report found it would be cost-effective to implement borough-wide speed limits and would cost about £3m to £4m for every borough.
As speed limits are imposed by local councils, London Mayor Boris Johnson was urged to provide councils with additional funds and conduct a pilot study.
The report recommended money for a pilot study be allocated from TfL's £63m road safety budget.
Green Party Assembly Member Jenny Jones, who led the study, said: "We are talking about saving lives and improving Londoners' living environment - surely this is justification enough for investing in a comparative pilot to test the best approach.
"Some boroughs are keen to expand on the successful zones they already have in place and I hope the mayor and Transport for London will put in the necessary funding and effort to support this."
Hugh Bladen, a spokesman for motorists' lobby the Association of British Drivers (ABD), said: "It's absolutely stupid. Driving around at 20mph and worrying about your speed is idiotic.
"It's not how fast they drive, it's how well they drive. The people who drive like lunatics are not going to take notice of this."
The report also suggested average speed cameras and signs as an alternative to speed humps on residential roads to enforce 20mph limits.
The committee looked at Portsmouth, which introduced a city-wide 20mph speed limit in 2006, and Graz in Austria as case studies for the report.