Glen Hellman was enjoying the comforts of riding Amtrak's evening Metroliner yesterday when an unexpected element entered the scenery. The forward part of the train moved off, leaving his car behind.

Hellman and two dozen other first-class passengers sat stranded in the club car -- the last of the six cars behind the Amtrak locomotive -- for about 20 minutes on tracks near New Carrollton after what an official later called an accidental uncoupling.

"It was like airplane turbulence, we just started bumping up and down," said Hellman, 31, of Potomac. "We stopped and the train kept going. Everybody in the car just stared at each other in disbelief."

Amtrak officials said the incident occurred about 5:10 p.m. and was caused by a malfunctioning coupler. Amtrak public affairs director John Jacobsen said the northbound train stopped a half mile down the tracks and backed up to pick up the passengers. The club car was left behind for later retrieval.

"This is not unprecedented, but it sure doesn't happen very often," Jacobsen said. "There was no danger, but it has the potential for not being a very good idea. Railroads don't like this to happen."

Hellman said he and other passengers sat comfortably during the wait. "The conductor opened the door to our car, and it was nothing but daylight ahead," he said.