Cyclists have taken to the streets to protest against changes to speed limits and junctions on Blackfriars Bridge.
A rush hour "flashride" was organised in a bid to get Transport for London (TfL) to reconsider scrapping a 20mph speed limit and restructuring the bridge's northern junction.
Later this year the speed limit will rise to 30mph and the lanes for motor traffic increased from two to three.
Cyclists claim the new designs give minimal consideration to their needs.
But TfL argues that the changes will allow Blackfriars Station to open at Christmas after a three-year upgrade, with a 60% increase in passengers and a tenfold increase in people entering and leaving the station.
Ben Plowden, TfL's director of better routes and places, said: "We've had to allow for that increase in pedestrian movement while allowing other people to go through the junction - cyclists, taxi drivers, taxi passengers - safely and efficiently and we think that's what the junction design will do."
The protests follow comments by the mayor of London, Boris Johnson, that "more work needs to be done" on the accessibility of cycling over Blackfriars Bridge.
The London Assembly has demanded a review of the speed limit and want TfL to re-examine how cyclists turn right at either end of the bridge.
During the flashride, the cyclists moved across the bridge en masse in a "go-slow" which temporarily held up traffic.
Cyclists are disputing TfL's claims that they make up 6% of traffic, arguing that the true figure given by the body's own 24-hour counts in 2010 was 16%.
The London Cycling Campaign - one of the backers of the Blackfriars Bridge flashride - has been arguing for a 20mph limit at Blackfriars to reduce road danger and help meet the mayor's aspirations to turn London into a cycling city.
Jim Davis, chairman of the newly formed Cycling Embassy of Great Britain, said: "By pushing ahead with this backwards design that gives minimal consideration to the needs of cyclists - who now outnumber cars on the bridge at peak hours - they are literally gambling with the safety of those wishing to get about by bicycle or on foot.
"It is responding neither to the all-party consensus of the London Assembly that its plans are unsatisfactory for pedestrians and cyclists, nor to Boris Johnson's own concerns about the problems faced by cyclists on Blackfriars Bridge.
"It should be of concern to all Londoners that the mayor and the GLA aren't in control."