PHILADELPHIA, JAN. 29 -- Investigators from the National Transportation Safety Board are waiting to question a railroad switch operator who fled shortly after the Washington-to-Boston Night Owl passenger train was directed down the wrong track at Chester, Pa., and slammed into maintenance equipment at nearly 90 miles per hour, derailing the train and injuring 24 people slightly.

Safety board member Joseph Nall said at a briefing tonight that an attorney for the switch operator, Tom Connor, had contacted Amtrak officials late this afternoon. But, Nall added, Connor had not yet been tested for drug and alcohol use. Nine other Amtrak employees involved in the crash were tested immediately after the accident, but results are not yet available.

Train service was delayed throughout the day on the Northeast Corridor, Amtrak's busiest route, as trains squeezed by on one of four tracks in the area near where the accident occurred.

The train's engineer and a baggage handler remained hospitalized last night after the overnight train carrying 160 people struck a track maintenance machine at 12:34 a.m., according to Amtrak and the NTSB. The other 22 injured people, including five Maryland residents, were treated and released, authorities said.

The train's two locomotives and one baggage car overturned, and a locomotive plunged down an embankment in an area about 15 miles south of Philadelphia where Amtrak's high-speed four-track main line is elevated above a densely populated area. The eight cars carrying passengers derailed but did not overturn.

"We were traveling along and all of a sudden the lights went out and I knew the train was off the tracks and the ties," passenger Orlando Dixon told United Press International. "The next thing that happened, I was knocked forward. I hit my head-on the seat in front of me and I fell to the floor. There were people screaming."

Amtrak, Federal Railroad Administration and NTSB investigators focused on the possibility of human error because the train should have been switched to another track to bypass the maintenance equipment, spokesmen said.

Connor was operating the track switches and signals from a nearby control tower in Marcus Hook, Pa., at the time of the accident, authorities said.

"The employee operator fled the scene of the accident. . . . It was not negligence on Amtrak's part," FRA Administrator John H. Riley said.

"The train crew was allowed onto the wrong track by that signal {controlled by the operator}," Riley said.

Nall said an Amtrak maintenance foreman took the track out of service after 10 p.m. and that the Night Owl slammed head on into the maintenance equipment on Track Two.

"The switches apparently were aligned for straight movement through Track Two," Nall said. He said investigators believe that a switch should have been pulled and the Amtrak train directed around the equipment on Track Two, but he said, it was too early in the investigation to know which track the train should have taken.

Amtrak spokesman Cliff Black said maintenance crews left a ballast regulator on the track. This is a piece of machinery, a little larger than a pickup truck, that adjusts the crushed rock beneath the tracks.

Nall said two workers on the ballast regulator jumped off when they saw the headlight of the Night Owl bearing down on them.

The ballast regulator is not designed to activate automatic stop signals, as would a locomotive or train, officials said.

During normal repairs, the maintenance crew foreman tells the train dispatchers to put a "hold" on the track, preventing other trains from passing through. The dispatcher, who routes the trains, is supposed to inform the operator in one of the control towers, located every few miles, to position the switches and set the signals to prevent trains from using the track.

Amtrak's dispatcher in Philadelphia said he ordered the operator at Marcus Hook tower to close the track before Connor started his work shift, and the dispatcher's statement is supported by records, said Amtrak spokeswoman Sue Martin.

Records from the earlier shift indicate that the previous operator had placed a device on the tower's control board to prevent anyone from inadvertently reopening the track, Martin said. Apparently, the device was removed, she said.

The NTSB has estimated that at the time the Night Owl's engineer hit the brakes, the train was traveling 87 to 90 mph, but Nall cautioned that the speed was estimated and that the actual speed has not yet been calibrated. The maximum speed allowed on that stretch of track for that train is 90 mph, Black said.

FRA estimated the damage at more than $2 million.

The overnight train left Union Station at 10:20 p.m. and was scheduled to arrive in Boston at 8:05 a.m. following stops in Baltimore, Philadelphia, New York, New Haven, Conn., and other eastern cities.

Parker reported from Philadelphia, Henderson from Washington.