Operator error caused a Silver Line test train to derail earlier this month, officials said Friday — the first such derailment since test trains began running on the line late last year.

Metro rail cars are being used to test the Silver Line tracks just west of the Wiehle-Reston East station. (Stephen Barna/Dulles Corridor Metrorail Project) Metro rail cars are being used to test the Silver Line tracks. (Stephen Barna/Dulles Corridor Metrorail Project)

No one was injured in the incident, which happened on a stretch of track near Wolf Trap. Pat Nowakowski, executive director of the Dulles Rail Project, said that the train traveled past its designated area and hit a device known as a “derailer,” which is designed to force the train off the track.

Nowakowski said that there are indicators along the track to tell operators they should stop because they have strayed beyond proper boundaries. But he would not be specific about what they were in this case. He added that there was no damage to the track or train in this instance.

The first phase of the rail line includes five new stops, including four that will run through Tyson’s. It is not clear when passenger service on the new line will begin. Officials at the Metropolitan Airports Authority, which is responsible for building the line, said in July that there would be an eight-week delay in completion — a development that could push the opening of the line into 2014.