An investigation into how a Metro train was allowed to leave the yard with too many cars has revealed that one employee was using drugs.

A green line train left the Greenbelt station shortly before 5 p.m. on July 31 with 10 cars. The transit system can only accommodate trains with a maximum of eight cars. A passenger notified the train operator of the extra cars about 20 minutes later.

As part of the investigation, the workers responsible for preparing the train underwent drug and alcohol testing. Metro spokesman Steven Taubenkibel says one employee tested positive for drugs. He says the worker is now in rehab and is not currently drawing a salary.

The incident is still under investigation, and Taubenkibel says no formal disciplinary action has been taken.