This seems a little "pie in the sky," to coin a phrase, but honchos in London want to construct a citywide network of elevated bikeways, over their teeming streets.
Sounds kinda cool. Practical? I don't know. However I do know that London acknowledges it has a major traffic problem - like any metropolis of its size. A few years back, they imposed a fairly steep toll on anybody who wants to drive his car into central London. Also, it would be bad if they built it, and people got the mistaken impression that since bicyclists have their "skyway," they no longer belong on city streets.