It has happened before.

On at least four other occasions a Megabus on the Toronto-Philadelphia route has taken the wrong turn and caused headaches for its passengers.

Only this time it was fatal.

Four people - including a South Jersey woman and a Temple student - were killed early Saturday when a double-decker Megabus bound for Toronto struck a railroad bridge in upstate New York.

Deanna Armstrong, 18, of Voorhees; Kevin Coffey, 19, an international business major at Temple; Ashwani Mehta, 34, of India; and Benjamin Okorie, 35, of Malaysia were killed in the accident which injured 20 other passengers.

The bus left Philadelphia at 10 p.m. Friday and was scheduled to stop in Syracuse and Buffalo before reaching Toronto at 7:15 a.m., said Dale Moser, chief operating officer of Coach USA, the parent company of Megabus.

But driver John Tomaszewski, of Burlington County, got lost in the suburbs of Syracuse. He missed the turn for the bus depot after exiting Interstate 81 North. Looking for a way back to the depot, Tomaszewski drove down Onondaga Lake Parkway checking his personal GPS unit for directions.

The GPS unit didn't tell him the CSX bridge crossing the Parkway had a clearance of only 10-feet nine-inches. The double-decker was 13-feet 9-inches tall. The crash sheared off the roof.

Wayward Megabuses are not uncommon on the Toronto-Philadelphia route, passengers said. On July 29, a southbound Megabus bound for Philadelphia went to Harrisburg instead.

On Aug. 2, a 10-hour trip stretched to 14 when the driver got lost twice. "At least he stopped in front of a low bridge," said passenger Dwayne Neal, a postal worker from Abington. "He called his dispatcher to see how low it was and then got the OK."

On Aug. 13, a northbound bus driver became disoriented north of Syracuse. The driver reoriented himself at a gas station, but not before falling about 90 minutes behind schedule, passengers said.

On northbound trip on Sept. 3, a driver got lost for 30 minutes at the Buffalo airport, said Joe Alberti, a teacher in West Philadelphia. "[It] was not even on the itinerary," Alberti said.

Moser, the Megabus executive, said he was unaware of those incidents. He said the company did not know how Tomaszewski got off route.

"It has nothing to do with the GPS system," he said.

The company discourages drivers from using personal GPS units because they are not designed for commercial use, Moser said. He said drivers go through 40 hours of classroom training, 10 hours of training behind the wheel and additional route training.

Moser said Tomaszewski, 59, had an excellent record and had driven the route nine times since mid-July. According to Syracuse.com, Tomaszewski received his commercial driver's license in December and began driving for the company in the Spring.

Reports of drivers going off route are not reported to the National Transportation Safety Board or the Department of Transportation, he said.

"It's an internal matter," he said. "If they go off route they're directed to contact 911 or to call our dispatch and then pull over and wait for instruction."

So why did Tomaszewski try to find his way back to the depot on his own?

"We're in the process of researching that," Moser said. "We don't have the answers at this point."

Contact staff writer Sam Wood at 215-854-2796 or samwood@phillynews.com.