Ever seen a short, bright green car running through a Metro station and wondered what it is and what it does? It’s Metro’s new track geometry vehicle, and it helps spot and fix small problems before they turn into big ones.

Metro’s track geometry vehicle. All photos by the author.

A track geometry vehicle monitors the physical condition of rails and other track infrastructure. Metro’s new vehicle entered service in 2013, and some have called it “The Pickle” because of its bright green color and shape. Metro employees prefer to call it the TGV, or even just “The Machine.”

Metro’s TGV uses lasers to identify problems with track geometry, like anomalies in gauge (the distance between two rails), alignment, or elevation and physical relation to platforms and third rail.

When the TGV identifies a potential problem, a team of employees inside the vehicle checks to see if the identified spot is an “exception,” which is when there’s an anomaly that’s not actually a safety issue. For example, there are places where the track gauge is wider than usual, but the particular spot moves around a tight curve where a wider gauge is necessary.

A curvature cheat sheet helps this track engineer know where there are exceptions in the system.

If it’s not an exception, the employees identify the problem spot by recording the associated chain marker, a yellow sign that indicates the distance from a central point (either Metro Center or Gallery Place) on each section of track.

The chain marker indicates this location is on the D section of the system, on track 2, and 22,300 feet from Metro Center.

Later, Metro’s track “walkers,” employees who walk along the tracks to look for defects, use this information to check out the potential problem spot and identify any need for repairs. The track “walkers” also do visual inspections without the aid of the TGV, but the TGV helps them find more subtle defects.

The TGV’s ultrasonic monitoring system.

The TGV also contains ultrasound sensors that can identify internal problems with the rails that could lead to cracks or corrosion. It also has forward-facing cameras that record video of the tunnel, which workers watch to look for structural problems. The TGV runs on diesel, so it can traverse the system even when rail power is down.

The TGV’s bright lights and cameras can illuminate structural problems with the tunnels too.

You have to be in the system at just the right time to catch the TGV in action. The TGV needs to run without stopping at around 35 to 40 mph to check track geometry, meaning it typically operates outside of rush hour so it doesn’t disrupt the schedule of faster-moving passenger trains or get stuck behind a train servicing a station. And for ultrasonic checks, the TGV needs to move at 10-15 mph with frequent stops so it can immediately confirm suspected problems. This sort of testing can only occur late at night, after the system is closed.

The track geometry vehicle team is aiming to make five ultrasonic testing runs and two track geometry testing runs of the system per year, which it’s proud to say is above FRA requirements. Prior to purchasing the TGV, Metro had to rely on contractors with somewhat incompatible vehicle sizes to make these runs. Employees say now that Metro has its own TGV, communication about defects and repairs is much smoother and clearer.


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Kelli Raboy works as a federal contractor supporting research on vehicle automation and communications. She loves all things cities, public transit, and rail. She lives in Navy Yard.