The doors on two Metro rail cars opened while a train was moving Tuesday morning, in a dangerous safety concern.

Now the transit agency is faced with the complicated decision of whether to pull at least a quarter of the system's fleet from service until all cars in the Rohr 1000 series can be tested, or risk another incident -- and possible rider injuries -- by keeping them running.

The incident happened shortly after 9 a.m. on the Red Line between Van Ness and Tenleytown on two of the system's oldest-model rail cars, the 1000 series, Metro spokesman Dan Stessel said. The blog Unsuck DC Metro first posted a rider's photo and email about the incident.

Metro's safety troubles
Tuesday's incident is the latest involving the 1000 series rail cars, which federal safety officials have warned about for years.
When involved in a crash, they telescope in on themselves, crushing riders, the National Transportation Safety Board has warned. The transit agency learned the warnings were valid during the deadly 2009 train crash, when nine people in 1000 series cars were killed.
Metro has ordered rail cars to replace the 290 cars of that model, but they won't all arrive until at least 2016.
The incident also was the latest frightening safety failure in the past six months. Brake equipment has broken off twice on two other model cars while trains were running. A defibrillator was found to have a dead battery when used on a rider suffering a fatal heart attack. And a train derailed last month near Rosslyn when a track worker failed to double-check that a clamp was in the correct position in a makeshift fix to the tracks.

No one was reported injured, Stessel said. Technicians met the train at Tenleytown and took it out of service, evacuating the riders. The six-car train was taken to a rail yard to be tested, because the controls for door openings run the length of the train, between multiple models of rail cars.

Doors opening on moving cars is a major safety problem as riders could fall out of the trains, exposing them to the electrified third rail and moving trains. It's especially an issue when trains are crowded, as passengers can be packed up against the closed doors. Tuesday's train was headed outbound at the end of the commute, but a rider's photo showed it was crowded enough that some people were standing.

"It's obviously a significant concern to us and to them," said Matt Bassett, chairman of the independent Tri-State Oversight Committee, which is charged with monitoring the system's rail safety.

Stessel said the incident was rare but noted that occasionally Metro gets reports of a partial opening of a door, a single door getting stuck a few inches open or flapping ajar. This incident was unheard of in recent memory, though, he said.

As of Tuesday evening, the remaining 290 or so cars of the 1000 model were still running. But Stessel said it's not clear if the problem was with that model of cars, the whole train or just those two cars.

"At this point, we have not identified a systemic issue that would cause us to consider a fleet-wide action," Stessel wrote in an email. "If a systemic issue were to be identified, we would not hesitate to take swift appropriate action to ensure the safety of our passengers and employees."

He acknowledged the agency is still testing the cars and had not determined what caused the doors to open.

However, when Metro officials had concerns in July 2010 that another model rail car's doors could open, the agency pulled 100 cars from service for about two weeks.

Officials had said all those cars were undergoing a "rigorous inspection, repair and testing process" even though they said at the time that no car doors had opened while trains were moving.

"This is a precautionary and proactive action to ensure the highest level of safety for our riders," then-interim General Manager Richard Sarles said at the time.

Stessel said Tuesday the 4000 series cars had a systemic failure that engineers had pinpointed, unlike the latest case. "There is no reason to believe it is anything other than an isolated incident at this point."