We bought the Brio / Plan City Road and Rail set last Christmas. I thought I'd get a standard road set to extend it a bit this year, but it seems they have changed the road. The old sort has two connecting bits on each end - they are now doing it with just one. If you contact Brio they will send you a free "adaptor kit". This is two short bits of road, each with one connector on one side, and two connectors on the other.
I've noticed a lot of places are still selling big blue boxes of road and rail with the old road system. So beware if you buy one, and expect to be able to add more road later.
I don't really want to spend £50 on road and rail as we've got plenty of road. Has anyone seen the old style road only for sale?