We've had them in West Yorkshire for quite a bit now. They were in fact
piloted in Hebden Bridge 2 or 3 yrs ago with some specially built Bluebird
Buses from the USA (by specially built I mean Right Hand Drive!) but they
have now been replaced by Optares,

I believe it has increased the uptake of the buses but there still seem to
be a heck of a lot of big cars around schools at 9am!

There's more at http://www.wymetro.com/BusTravel/MyBus/