The notion of enjoying a cold one aboard a rush-hour commuter train leaving Manhattan may seem like a time-honored tradition, evoking visions of communal bar cars or perhaps a cocktail hour spent in solitude at one’s seat. But after midnight on weekends, the specter of alcohol aboard Long Island Rail Road trains carries a far more malevolent overtone; passengers described them as the “drunk trains,” characterized by fights and boisterous behavior. In March, passengers were accused of attacking two conductors.

The disorder has led the Metropolitan Transportation Authority to test a ban that will prohibit riders from bringing alcoholic drinks onto Long Island Rail Road trains leaving Pennsylvania Station on Friday and Saturday nights between midnight and 5 a.m., effective May 14.

Sam Zambuto, a spokesman for the railroad, said that the alleged attacks were “the impetus for forming a task force to discuss this issue.” The ban, for an indefinite period, will be enforced by the Metropolitan Transportation Authority police.

At 4:30 a.m. on March 25, a Sunday, a 19-year-old man was arrested on charges of attacking a conductor at the Woodside station; the police said that alcohol was involved. The next Thursday, a conductor was alleged to have been punched in the face; an 18-year-old man and a 17-year-old woman were arrested. It is unclear whether alcohol was involved in that attack.