Ok, take Oxford Street as an example.
It’s a single carriageway road with one lane of traffic eastbound and one lane westbound. When roadworks take place and remove one of these lanes all the buses & taxis have to be diverted. How will you fit a dedicated cycle lane in here? Would you permanently divert the traffic along the whole length of the road and make it one way only?
Then you’ve got the cost of installing the kerb stones along the length of the road.
Then you’ve got the cost of the signage.
Then you’ve got to consider if the traffic lights need changing (either phasing or the addition of low level lights for the cyclists).
Then you’ve got to consider the knock-on effect of the diverted traffic on the surrounding streets.
Then you’ve got to consider the resistance from the retailers that half the number of buses & taxis now stop outside their shops.
Then you’ve got to get it passed by a planning committee and funded from somewhere…
Where roads are being completely re-modelled, then yes, I can see there is an argument for trying to get something done, but with regard to retrofitting onto the already packed central London roads, I simply can’t see it happening.