Making sure all 659 miles of the New York City subway system's tracks are in good working order is a herculean task. Amazingly, for most of the subway system's 111-year history, that job fell entirely to human inspectors. "Trackwalkers," as their name implies, walked the length of the rails while trains were operating, visually surveying them for damage.

The New York Metropolitan Transit Authority (MTA) still conducts human inspections twice a week, as it has since 2006. But it also has the benefit of a much more futuristic, automated system: track geometry cars.

Shown off in a new video the MTA released last week, these specialized train cars are festooned with a variety of lights, sensors, and cameras designed to measure the condition of the rails and spot any defects before they cause accidents. The cars pay special attention to track gauge, the distance between the two running rails that can fluctuate and cause derailments. Onboard the diagnostic train, a small staff of engineers reviews the data gathered by the system in real time with the help of 30 onboard computers.

The MTA's geometry car system is manufactured by Plasser American in Chesapeake, VA. A 2013 Federal Transit Administration study of the system found that it outperformed human trackwalkers in accuracy and total number of defects uncovered. The study also reveals lots of detail about what the geometry car sees and how it presents data, including a combination of video captures and numeric data in spreadsheets.

The MTA has four track geometry cars running constant inspections, according to Gizmodo. Yet because the subway system is so large, they can cover each length of track only six times per year.

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