There's also the slight quirk of geography that it's next to the Thames, so therefore at the bottom of a hill, almost completely flat. TfL had the good fortune

There's also the slight quirk of geography that it's next to the Thames, so therefore at the bottom of a hill, almost completely flat. TfL had the good fortune and opportunity to repurpose two lanes of Upper Thames St. and Victoria Embankment (one single road) into cycle lanes, and also Southwark Bridge. Without that last part, there's pretty much no other major 'through' routes that could be made safe for cyclists in the City. If there aren't any protected bike no one uses them. The vast majority of journeys into the City are along that new cycle 'superhighway'.