The Mayor's promise follows commitments last year to spend £913m over a decade on a Cycling Vision.
This £300m funding announcement  comprises part of the overall budget and includes the cash allocated to the cycle superhighway programme.
Designs for the first of these junctions will emerge in the next few months, but experience elsewhere shows that good design is hard to achieve unless roadspace is reallocated from general traffic lanes. The Mayor has promised to "maintain [the] traffic function" of these gyratories, which may reduce the scope designers have to provide adequate space for cycling.
The Mayor of London, Boris Johnson, said: “These road junctions are relics of the Sixties which blight and menace whole neighbourhoods. Like so much from that era, they’re also atrociously-designed and wasteful of space. Because of that, we can turn these junctions into more civilised places for cyclists and pedestrians, while at the same time maintaining their traffic function.”
Blackfriars Bridge's northern junction is to be redesigned for the third time in a decade, which represents a significant waste of resources. Exact details on the changes to be made will emerge over the next few months, but many of the junctions are set to be rebuilt before the next Mayoral election in 2016.
The announcement was criticised by London Assembly Member Darren Johnson, from the Green Party, who pointed to the fact that the this announcement represented a reduction to 33 junctions from over 100 previously announced, saying:
"Setting out a grand vision for cycling is all very well, but at the end of the day the Mayor will be judged on delivery. By downgrading his junction review programme so drastically he will end up delivering less than a third of the junctions he promised by the time he leaves office. If a lack of funds is the problem, the Mayor could boost funding to tackle dangerous junctions in his next budget. If a lack of expertise is the issue, he could easily get Dutch cycle engineers to redesign our dangerous black spots. TfL can deliver major schemes such as Crossrail. It’s time they gave cycling the same kind of treatment."
In Southampton, a newly redesigned junction  has run into criticism from campaigners and local cyclists for failing to provide the safe conditions that were initially promised, with cycle lanes narrower than planned, and no dedicated cycling traffic lights.