So many cookies...
London also has a particular hazard for cyclists... ...in that many streets have guard rails to protect pedestrians from traffic
Not particular to London; not particularly many; and more likely to protect traffic from pedestrians than vice-versa
Fundamentally the idea suffers by doubling up the effect of the current dual-direction cycle superhighways. It really really fucks up traffic flow. Every Traffic Lighted T junction that has 5 phases of traffic suddenly needs more, to allow for segregated cycle traffic to make the same motor vehicle manouvers; and every T Junction now needs traffic lights.
Given the Dutch have an aversion to round abouts, traffic lights are all pervasive, and some how the cycle infrastructure works. This is largely because the cycle lane on the right of the traffic is treated as part of the traffic, and signalled accordingly. It does mean that turning left requires you to go through 2 sets of lights on a bike, tho in many cases a cyclist will just go straight across and left, a bit like a scramble crossing.
Railings along the edge of roads are evil and should be banned out right. They have been shown to have caused fatalities where cyclists have been crushed against them, and the benefits of stopping pedestrians falling into traffic are hard to prove. They are a symptom of private car supremacy, which we should be taking all measures to crush.
As for the original topic. Ask yourself: if it's such a good idea, why has it not been done in the one country where every possible experimentation of bike infrastructure seems to have been trailed?
The main issue I see with most UK cycle path implementations is that they have give way signs at every bloody side road, which is just stupid. The cycle lane should go straight across the side road, at the same level. This puts a defined speed table/bump at the end of the side road, which also helps signify right of way.
As for the specific issue with London cycle superhighways? They seem to have been drawn by someone who thinks motorways are a good idea, and owns some crayons. (Incidentally the same type of people seem to be behind HS2). But I could rant at length about this, but I'd just be preaching to the perverted.
J