Metro officials told the board Thursday that speed caused an August incident in which a test train derailed on the soon-to-open Silver Line.
The train was traveling 19 miles an hour and it should have been going 5 miles per hour, the board was told.
There were no injuries. The derailment is one of several incidents that have occurred in the testing of the Silver Line, which is set to open early next year. The train operator was “disciplined and retrained,” Metro officials said.
Officials also said several factors contributed to another August incident in which a train derailed near the Rhode Island Avenue station.
A train was carrying a 1000-series rail car that had caught fire in a May incident in Silver Spring. The rail car was being taken to Greenbelt where it would eventually be turned to scrap metal.
A piece of equipment on a rail car called a truck, or a wheel set, which provides suspension, propulsion and braking to trains was part of the cause of the derailment. The rail car had a “dummy truck” on it that did not have those systems on it so it was lighter than a normal truck would be, officials said.
The dummy truck is “free-flowing wheels,” which generally amounts to the “equivalent of having a car in neutral,” according to Metro spokesman Dan Stessel.
“That created a condition where it was possible for the train to climb the rail,” Stessel said.
Two rail cars derailed in the incident.
“The load wasn’t uniformly distributed,” said Rob Troup, who is in charge of Metro’s rail operations. “It road up, then came off the rail head. That was the primary point of derailment.”
Metro said it has stopped using dummy trucks in moving trains as a result of the incident.