In fact I don't think these buses even operate in London anymore. I lived in London from 1985-88 and often caught these Routemaster buses which were so convenient because when they were stuck in traffic you could just jump on the back which is open. Of course this meant you had a driver and a ticket collector on the bus. Now there are just drivers, so there's no open back and I imagine you have to get on at the bus stop too, even if the bus is stuck in traffic! Although I am happy to be corrected by any Londoners!