The driver of a Toronto-bound bus was using a personal GPS when he drove the double-decker vehicle into a low railway bridge in central New York, a crash that resulted in the death of four passengers.

Onondaga County Sheriff Kevin Walsh said John Tomaszewski, 59, was using his own device and not the one installed on board the Megabus when he crashed into the railway bridge during an overnight trip between Philadelphia and Toronto.

Four people were killed and 20 others injured when the crash tore apart the second level of the bus, Saturday morning. Megabus officials confirm the driver was off his prescribed course at the time of the accident.

Walsh told The Associated Press they are trying to determine whether Tomaszewski was holding the device or listening to it at the time of the crash.

Officials say the driver had made a wrong turn off Interstate 81 in Salina, a suburb of Syracuse, N.Y., but could not say how he missed signs warning of the low-hanging bridge.

The Megabus was heading for Toronto at the time of the crash, but was supposed to make a stop in Syracuse.

Don Carmichael of Coach USA, which operates Megabus, said the driver "obviously made a wrong turn" because at the time of the crash the bus had deviated from its usual route.

He said Tomaszewski had driven the correct route numerous times.

Seven Canadians were among the 28 passengers on the bus, all of whom survived the crash with minor injuries. Tomaszewski sustained some injuries, but has been released from the hospital.

With files from The Associated Press