Our rail system in the UK includes more than 10,000 miles of track that, until relatively recently, had to be inspected at a walking pace. This laser-blasting, track-inspecting locomotive, however, does so faster than a speeding bullet (train).
The New Measurement Train (NMT) is one of 17 track-inspecting trains employed by Network Rail. Its bright yellow livery and blistering 125 mph pace earned it the nickname "the flying banana". It sandwiches two messing cars, two operations cars, and a meeting car between a pair of MTU V16 4000 R41 diesel-electric engines.
The operations cars are packed with sensory equipment designed to spot the slightest faults in the tracks. This includes a Track Geometry System, which measures the relative orientation between each pair of tracks using laser track scanners and seven high-res video cameras; an overhead line inspection system; and the Plain Line Pattern Recognition (PLPR) system, which looks for "abnormal join gaps, abnormal expansion join width, railhead defects and cracks, fishplate defects, switch area defect recognition, sleeper defects, missing fasteners and weld clamps that should have been removed," according to the system's creator, Rail Vision. Basically anything that could be big trouble, either right now or a few days, months, years down the line.
While the other track-inspecting trains in Network Rail's stables only travel about 30 mph, the NMT's 125 mph pace leaves them in the dust. At that pace, the NMT was able to spot a whopping 33,000 faults requiring additional inspection in September of this year alone. [The Register - Rail Vision - Network Rail - Wiki]