It’s WMATA’s track geometry vehicle (TGV), a manned, diesel-powered Metrorail car that’s painted a vivid emerald hue.
Why it exists: Informally known as “The Pickle,” the TGV trawls the Metro system flagging potential problems. It uses ultrasound to look for defects inside the tracks and an infrared camera to detect issues with the third rail. It also makes sure the two outer rails are always the same distance apart.
When to spot: The Pickle works about three weeks per month, and can be anywhere in the Metrorail system. Look for it zooming through stations between 10 a.m. and 3 p.m. on weekdays, or try to catch it in repose during morning rush hour. As you ride the Blue Line from King Street to Van Dorn, look to the right and scan for green among the parked trains at the Alexandria rail yard.
Why green? “A lot of us asked that same question and we haven’t been able to come up with a very logical answer,” says WMATA assistant chief engineer Andy Off. “It does run during revenue hours and it moves through stations, so we wanted it to be overwhelmingly clear that it’s not a normal revenue car.”