They're clumsy devices that arguably don't work on the real problem - motorists who charge over them: drivers of company cars and especially vans; stolen or uninsured cars; un-MOTd cars and worst of all: bin lorries; so they're not a solution if your aim is to stop speeders. And they cause loads of pollution, as motorists grind along at high revs in 2nd gear, accelerating away after each bump. Cyclists hate the full width ones because they wreck your wheels; they hate the cushion ones because drivers swerve without warning to straddles them. And to motorcyclists, on a dark night, in the wet, they're lethal.