Commuters are having to wait more than ten minutes longer than ten years ago on some lines because of heavy traffic, Trentbarton has said.
It claims some of its Nottingham and Derby routes take a third longer than they did in 2009, with "huge volumes" of sole-occupancy cars, and said this "can't continue".
They called on the councils to give them priority on lanes and traffic lights in a bid to get more people to use their service than drive themselves in.
Nottingham City Council said it already has 12 miles of bus lanes and along with Derby is looking to create bus routes on the A52. Derby City Council said it has invested millions to improve bus transport.