On January 4, 1987, two trains collided on Amtrak's Northeast Corridor main line near Chase, Maryland, United States, at Gunpow Interlocking. Amtrak train 94, the Colonial, (now part of the Northeast Regional) traveling north from Washington, D.C., to Boston, crashed at over 100 miles per hour (160 km/h) into a set of Conrail locomotives running light (without freight cars) that had fouled the mainline. Fourteen passengers on the Amtrak train died, as well as the Amtrak engineer and lounge car attendant.

The Conrail locomotive crew failed to stop at the signals before Gunpow Interlocking, and it was determined that the accident would have been avoided had they done so. Additionally, they tested positive for cannabis. The engineer served four years in a Maryland prison for his role in the crash. In the aftermath, drug and alcohol procedures for train crews were overhauled by the Federal Railroad Administration (FRA), which is charged with rail safety. In 1991, prompted in large part by this crash, the United States Congress took even broader action and authorized mandatory random drug-testing for all employees in "safety-sensitive" jobs in all industries regulated by the U.S. Department of Transportation (DOT) including trucking, bus carriers and rail systems. Additionally, all trains operating on the high-speed Northeast Corridor are now equipped with automatic cab signaling with an automatic train stop feature. Several safety issues were identified with Amfleet cars as well.

At the time, the wreck was the deadliest in Amtrak's history. It was surpassed in 1993 by the Big Bayou Canot rail accident in Alabama where 47 died and another 103 were injured.

Amtrak Train 94 (the Colonial) left Washington Union Station at 12:30 pm (Eastern time) for Boston South Station. The train had 12 coaches and was filled with travelers returning from the holiday season to their homes and schools for the second semester of the year. Two AEM-7 locomotives, numbered 900 and 903, led the train; #903 was the lead locomotive. The engineer was 35-year-old Jerome Evans.

After leaving Baltimore Penn Station, the train's next stop was Wilmington, Delaware. Just north of Baltimore, while still in Baltimore County, the four-track Northeast Corridor narrows to two tracks at Gunpow Interlocking just before crossing over the Gunpowder River. The train accelerated north toward that location.

Ricky Lynn Gates, a Penn Central and Conrail engineer since 1973, was operating a trio of Conrail GE B36-7 locomotives light (with no freight cars) from Conrail's Bayview Yard just east of Baltimore bound for Enola Yard near Harrisburg, Pennsylvania. Gates was later determined to have violated several signal and operating rules, including a failure to properly test his cab signals as required before departure from Bayview. It was later discovered that someone had disabled the cab signal alerter whistle on lead unit #5044 with duct tape, muting it almost completely. Also, one of the light bulbs in the PRR-style cab signal display had been removed. Investigators believed these conditions probably existed prior to departure from Bayview and that they would have been revealed by a properly performed departure test.

Gates and his brakeman, Edward "Butch" Cromwell, were also smoking cannabis cigarettes. Cannabis can alter one's sense of time and impair the ability to perform tasks that require concentration. Cromwell was responsible for calling out the signals if Gates missed them, but failed to do so.

Amtrak train #94 was north-bound on track #2 of the electrified main line leading to Gunpow Interlocking. As Amtrak was approaching the interlocking, a “light” Conrail consist of three diesel-electric freight locomotives was running north-bound on parallel track #1 in a ferrying move (see photo to right for track identification). Gunpow Interlocking is fully signaled to govern train movements, with all signals mounted on signal bridges straddling the tracks, placing them in clear view of oncoming trains.