The mayor said safety would not be compromised at pedestrian crossings
Pedestrians could be given a countdown to tell them how long they have left to cross the road at some London crossings under plans proposed by the mayor.
A digital countdown, which would need permission from the Department for Transport, would inform pedestrians how long they have left to cross the roads.
At some crossings it will mean people will also be given less time to cross.
London Labour Assembly member Val Shawcross warned it would make the city less pedestrian-friendly.
Mayor Boris Johnson said the proposal was being put forward to make junctions more efficient.
If the pedestrian countdown goes ahead, it will be the first one of its kind in the UK.
A Department for Transport (DfT) spokeswoman said: "We are in discussions with TfL about their pedestrian countdown proposals. We have recommended that they carry out research and off-street trials to assess the potential impacts.
"The DfT would need to be convinced of the benefits of such a measure before it could approve it could be implemented on-street."
The mayor said any changes made to any traffic signal timing would not affect the minimum amount of time needed by law to enable a pedestrian to cross the road safely - 1.2m a second, which was based on Department for Transport (DfT) guidance.
Since July, Transport for London (TfL) has already altered timings at 150 sets of lights across London, out of the city's total of 6,000.
It said it was part of a project to try and ease congestion on the capital's roads.
A TfL spokesperson said the remaining lights would be reviewed on a "case-by-case" basis over the next six years.
A spokesperson for the mayor said: "The mayor shares the frustration of thousands of Londoners about the snail's pace at which traffic moves through the streets.
"One of the things he is doing to address this is asking Transport for London to review the timings of traffic signals in the capital to ensure they are kept as efficient as possible."
But Ms Shawcross, chair of London Assembly's Transport Committee, said: "The mayor is favouring the driver and is rowing in the wrong direction.
"He said he wants to make London more pedestrian-friendly but he is fact doing the opposite."
She said the mayor should be encouraging more walking and less private vehicle and added more pedestrian crossings were needed in London generally.