Lambeth will not follow other London boroughs to introduce 20mph speed limits on all residential roads, it has emerged.
Campaigners have called for the measure, which is in place in neighbouring Southwark, to combat Lambeth's high number of road casualties.
Although serious accidents have almost halved since the mid-1990s, the borough still has the third-highest number of road incidents in London.
An 86-year-old woman was killed in Tulse Hill in November and in March young ballerina Charlotte Leatherbarrow, 12, died after getting trapped under a double decker bus in Herne Hill.
Green Party London Assembly candidate Jonathan Bartley is leading the campaign for a blanket speed reduction on residential roads.
He said: "Why on earth is Lambeth council not introducing a measure that can save lives now?
"We have known for years that one far more likely to be a fatality at 30mph. It's absolutely common sense."
He added that a lower speed limit also benefits traffic flow and the environment.
The Lambeth Transport Plan, which was approved in December, says the proposal was rejected due to enforcement problems.
Councillor Nigel Haselden, Lambeth Council’s cabinet member for transport, said: “We are committed to working with communities to decide how to manage speed.
“This includes using a combination of 20mph zones, tree planting and ‘green shields’ to cut traffic speeds. As well as being measures that residents want they are also improving the look of our streets.”
A petition in favour of the a 20mph speed limit in residential streets is available to view online here.