Cyclists have dismissed Mayor of London Boris Johnson's announcement of two new cycle superhighways through the city as a "marketing gimmick".
From May 2010, two corridors of cycle lanes will lead from south Wimbledon to Bank and Barking to Tower Hill.
But Transport for London (TfL) admitted much of the route would not be covered by the lanes through lack of space.
The pilot routes are the first of 12 superhighways earmarked to be developed before the Olympics in 2012.
TfL is consulting with the eight boroughs they will pass through to finalise the exact layout.
Mr Johnson, who rides to work from Islington to City Hall, said: "I'm not kidding when I say that I'm militant about cycling, and these superhighways are central to the cycling revolution I'm determined to bring about.
"No longer will pedal power have to dance and dodge around petrol power - on these routes the bicycle will dominate and that will be clear to all others using them."
Where possible, cycle lanes will be separated from motor traffic and painted blue.
But Transport for London told the BBC space constraints made it impossible to build cycle lanes the length of the routes.
They said it was too early to confirm what percentage of the superhighways would comprise cycle lanes.
Andreas Kambanis, who writes the London Cyclist blog, said: "It sounds cool but it's not exactly groundbreaking.
"It is a bit more of a marketing gimmick than a real help for cyclists.
"But anything that raises awareness of cycling - and gets drivers to take a bit more notice of bikes - is a good thing."