I remember riding round Swindon on my motorbike some time around 1990 - one of those foolish things you do when young! - and some of the zebra crossings there were raised, like a large, stripy speed bump. I think these were removed sometime later. In some other countries speed bumps are often placed on the approach to zebras - and those tend to be proper bumps, like half a mains water pipe tarmacced into the road, as opposed to the rather mild ones favoured here. I'm not sure which of these methods works best, if either. They also seem to be installing some zebras in Brizzle which are flush, no step up/down the kerb, but the gradient is gradual so vehicles don't experience any bump. Good for wheeled footway users, obviously, but they haven't finished them yet so I'll reserve judgment for the time being.