A really relevant and interesting piece of work by my landscape colleagues can be read here Bridge-it. The idea is as follows:
Our proposal unlocks inaccessible transport corridors whilst retaining their active use as an essential transport network. A new green infrastructure network will extend across the entire city, opening up walking and cycling routes along established major lines of movement. It will link communities, parks, transport hubs and create new development potential; linking central London transport hubs with London’s parks and open spaces with green linear parks built over, under and beside railway lines.
This type of initiative could make a huge difference to cities like London where the road infrastructure is not suitable for mixed traffic, but where the rail network creates substantial links between major elements of the city. Rail and cycling mix well as both are ideally flat or have level gradients, and crossings are kept to a minimum. This is the kind of idea that could make cycling really work in London.