The Central London grid

TfL are really pleased with the 'armadillos' on Royal College Street. Their view is that this light segregation means riders can easily move out of the bike bit onto the road. It is also easily tweaked and can be widened etc since it is not made of stone.

I think it's more than just the ability to "tweak". Rapid prototyping, which can be reversed or abandoned is increasingly seen as a really valuable tool in designing just about anything. It's really difficult to predict how people will respond to a design (especially in a highly interconnected system like London streets). So being able to just do it cheaply and quickly with a bit of paint and/or some moveable planters is a hugely valuable thing.