Derailment Near Penn Station Snarls Train Travel In a train tunnel just east of Pennsylvania Station, the two middle cars in a 10-car Long Island Rail Road train slid off the rails. Passengers were evacuated without significant incident. Though about 500 feet of track sustained damage, the derailment, which occurred on Monday night, was by all accounts minor. And yet throughout the Northeast, the ripple effects of the accident were felt. Amtrak trains were snarled as far away as Boston and Albany; New Jersey Transit trains were delayed, and Long Islanders were sent into a scramble for whatever combination of subways, car services and neighborly kindnesses would get them home. Some trains remained in holding patterns for hours, at times zigzagging about the region for reasons that remained unclear to riders. "Occasionally they would say they were about to pull in or back up to a place that was "safer," " recalled Amy McIntosh, a senior fellow with the New York State Education Department, who was riding an Amtrak train from Albany to Penn Station on Monday. Safer? So we weren't safe? Ms. McIntosh said her train left Albany around 7:45 p.m. She stepped off at 1:15 a.m. The episodes were an unwelcome reminder that at the nation's busiest rail hub, with so many transit fates intertwined, even the smallest hiccup can upset the machinery. The derailment initially obstructed two of the four East River tunnels that connect to Penn Station. Though the Long Island Rail Road uses them most, Amtrak's Empire and Northeast Corridor services also rely on the tunnels. And New Jersey Transit uses the tunnels to reach Amtrak's Sunnyside rail yards in Queens, where many trains are stored and serviced. "It took place in a spot that's particularly problematic," Aaron Donovan, a spokesman for the Metropolitan Transportation Authority, said of the derailment, adding, "That's just the nature of the configuration of tracks." While most other service had returned to normal by Tuesday, the authority canceled 21 of its evening-rush trains out of Penn Station - 16 percent of its service. In the morning, 34 rush-hour trains were canceled, diverted or terminated early. Caryl Kahn, 56, who commutes to Midtown from Rockville Centre in Nassau County, said the derailment had forced her fellow travelers out of their element. "There are people, particularly those from the suburbs, who are afraid of the subway," she said. So there's all kinds of panic. On Tuesday, expecting delays, she left shortly after 7 a.m., about 40 minutes earlier than usual, and boarded a train bound for Jamaica. Then she tried a maneuver practiced by few but the most expert subway riders: As fellow riders poured onto the subway at Sutphin Boulevard, headed for Manhattan, she took an eastbound E train one stop, to Jamaica Center, traveling in the opposite direction. When the train turned west, heading back to Manhattan, she had secured a seat before the next crush of commuters came on board. Others opted out altogether. Erica Glass, who typically travels between her home in Plainview, N.Y., and her job in Lower Manhattan using the subway and the Long Island Rail Road, said she took a car service home on Monday after hearing about the derailment. It was $68 well spent, she said. If travelers had flocked to the Long Island Expressway in their own cars on Tuesday, it would have been difficult to gauge. "The L.I.E. is always jammed," said Samuel I. Schwartz, the traffic engineering expert known as Gridlock Sam. It's hard to tell if it's a longer parking lot. Robert Guariglia, 63, from Deer Park, N.Y., said he knew from the moment he heard about the derailment that he would work from home on Tuesday. "I've been commuting for more than 20 years," he said. It's been very unusual that the problem gets resolved in a day. For those who did ride the rails on Tuesday, expectations were tempered. "There have been times I wished for Wi-Fi on the L.I.R.R.," one rider wrote on Twitter on Tuesday. Today I just hope the train can stay on the tracks.