[sigwinch28]

Measurement trains filled with cameras and LIDAR

For example, in the U.K.:

https://en.wikipedia.org/wiki/New_Measurement_Train

[jen729w]

https://en.wikipedia.org/wiki/Doctor_Yellow

[user_7832]

LIDAR is good, but as another commenter pointed out, Ultrasonic Flaw Detection (USFD) is the gold standard for crack/flaw detection.