A bus had to stop short on Storrow Drive Thursday after the driver realized that the vehicle could not fit under the Boston University Bridge, State Police said. The driver stopped at 6 p.m., and the bus was forced to wait until after rush hour to move, State Police Trooper Thomas Murphy said. At about 8 p.m., the driver was able to back the bus up and exit Storrow Drive. The bus did not hit the bridge and no one was injured, although the evening commute was affected, Murphy said. No further information was immediately available.Melissa Hanson can be reached at email@example.com or on Twitter @Melissa__Hanson.