The US Federal Railroad Administration is hoping that a new apparatus it is testing will prevent many of the derailments that take place on US railways every year. The gadget ‘taps’ the tracks with a laser pulse, and listens for echoes to help it locate and identify microscoping flaws in the rails. Similar techniques have been used before, but the current system uses transducers that have to stay in contact with the rails, meaning that the scans have to be done much more slowly.