Derailment at Farragut North a safety system success

This morning’s commute was marred not only by the snow drifts spread across the region, but also by a minor derailment on the Red Line at Farragut North.

While there was some confusion in initial reports, some things have become clear about the accident. The derailment itself was caused by a safety device known as a “derailer,” which prevented the train from entering a track potentially occupied by another train.

This incident occurred at the northern end of the pocket track immediately north of the Farragut North station. The train that derailed was carrying about 350 passengers in the direction of Shady Grove. Three minor injuries were reported, and one passenger was transported to the hospital.

Because the accident occurred in the pocket track, the train did not foul either of the main tracks, and a few trains passed by in both directions before the station was closed. Passengers were eventually rescued by being moved to the rear four cars, which returned to Farragut North.

The train was bound for White Flint station. White Flint was to be the terminal because Twinbrook, Rockville, and Shady Grove remained closed due to snow accumulation on the tracks. After stopping at Farragut North to allow passengers to board and alight, the train began to head north toward Dupont Circle. Immediately north of the Farragut North platform, there is a pocket track.

This pocket track is typically used to store trains or allow them to turn back in the direction from which they came. In some cases it is used to allow trains to switch between the inbound and outbound track.

For some reason, the switch was set to allow the northbound train onto the pocket track (at “A” in the diagram). It is unclear at this time why the switch sent the train into the pocket. However, the operator continued traveling toward Dupont Circle at a low rate of speed. This low speed would have been enforced by the Automatic Train Control (ATC) system.

The pocket track is about 600 feet long, the same length as a Metro platform. At the northern end of the pocket (at “C” on the diagram), is another switch. This switch enables trains in the pocket to switch to Track 1 or Track 2. At this point there is a signal and derailer. Since the derailer was engaged, the signal should have been red - assuming there were no mechanical or electrical problems with the device. The train operator should have been able to see the red signal when the train entered the pocket (at “B”), at least 600 feet away.

Now, the signal at “C” would only show a clear to proceed aspect if several conditions were met: The switch at “C” is set to the right, the switch at “D” is set for the pocket turnout, and the track immediately north of “D” is clear. Or, the switch at “C” is set to the left, the switch at “E” is set for the pocket turnout, and the track immediately north of “E” is clear.

Otherwise, the signal would show a red aspect and the derailer would be engaged.

The derailer works by literally derailing the train. Basically, if the switch is set in a manner which will direct the train into danger, the derailer is engaged. It is automatically operated by the signal system and, when engaged, is placed flush against one of the running rails.

It essentially acts as a ramp for one of the wheels, lifting it up to the level of the rail. It then channels that wheel toward the outside of the track, which causes the wheel truck to drop so that one wheel is off the trackbed and the other wheel is in between the running rails. This creates additional friction, and should stop a train even if braking power has been lost.

Of course, derailers can fail. One of the most tragic cases occurred on September 15, 1958 when a commuter train bound for the ferries to New York City ran off the end of an open drawbridge. The accident killed 48, including Kurt Vonnegut’s brother-in-law. He references this accident in his works.

As the train approached the CRRNJ Newark Bay Lift Bridge, it ran through three red signals and hit a derailer 450 feet before the bridge. Despite being derailed, the two locomotives and three passenger cars skidded off into the bay.

In today’s derailment, however, the derailer worked as intended. In fact, not only did the derailer prevent a collision or damage to misaligned switches, it also prevented the train from fouling either main track. However, while this event saw the safety system avert potential disaster, it is not clear why a potentially dangerous situation was allowed to progress so far. Many questions remain.

All of Metro’s riders can hope that the root cause will quickly be determined so that future instances can be prevented.