Beneath the city that never sleeps, MTA's "track geometry car" worms its way through New York's subway tunnels, using a menagerie of sensors and cameras to inspect the tracks. Geoff Manaugh at Bldg Blog is captivated:
But it's hard not to be captivated by the idea of some blindingly well-lit behemoth vehicle maneuvering around beneath the city at night, all lasers, mirrors, lenses, and prisms—a surreal, moving garden of repurposed photographic equipment and motion-capture technologies from different historical eras—scanning the geometry of the metropolis from below, down to thermal flaws in the very metal it passes over.
I find this use of high-tech tools to improve a low-tech transportation system fascinating. If you want to geek out, there are a bunch of videos of this train on YouTube.