Track recording car Pic credit : Mahesh k

A track recording car is an automated track inspection vehicle on a rail transport system used to test several geometric parameters of the track without obstructing normal railroad operations. Some of the parameters generally measured include position, curvature, alignment of the track, smoothness, and the crosslevel of the two rails. The cars use a variety of sensors, measuring systems, and data management systems to create a profile of the track being inspected.
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Every route has a periodic inspection of track quality using the track recording car. That's why we regularly see posts on IRI about RDSO coaches visiting some station with a WAP5 loco etc.
It's just that the Track recording coaches are managed by RDSO, who will use the data for their own research and design operations.