The latest issue of "Physics Today" gives a diagram of where the energy
produced by an engine of a midsize vehicle.  Following, is the break down
(parenthetical numbers are for highway driving - as opposed to urban 
driving).  Assuming 100% of energy is derived from the engine:

	62.4 (69.2)% 	Engine losses
	17.2 (3.6)%	Standby
	 2.2 (1.5)%	Accessories
	 5.6 (5.4)%	Driveline (-train?) losses
	 2.6 (10.9)%	Aero (much larger for our busses!)
	 4.2 (7.1)%	Rolling
	 5.8 (2.2)%	Breaking

which leaves 5.8 (2.2)% (from the breaking category) of the total
energy produced by the engine to be translated into kinetic energy....

what's the efficiency for a '65 ucrobus?

christian