The familiar 30mph speed limit sign in London could be replaced by a 20mph sign if the London Assembly Green Party's proposals are approved.
Road safety experts are supporting the plans to bring down the speed limit across much of the capital within the next three years.
Jenny Jones, the mayor's Green road safety adviser, said: "Making 20mph the normal speed limit would save lives and money and give a major boost to cyclists, who would feel safer."
The mayor is reported to be in favour of the 20 mph speed limits, but is yet to be persuaded over whether they should be implemented across London.
Research reveals that reducing the speed limit by ten miles per hour could cut the number of road deaths by around half.
As a compromise, many speed bumps – the bane of numerous motorists – will be removed.
But not everyone is in favour of the proposals. Andrew Howard, the AA's road safety expert, told Autocar: "We are very worried about the law of unintended consequences.
"Many motorists will start to use tiny side streets for the most direct route if they are restricted to 20mph on main roads. And you could end up with the situation where the most inappropriate roads become much busier."
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