Detectors
Several railroads have these type of systems.
But wait there's more!
There are also wheel impact detectors. Originally intended to detect flat spots, the UP found that by measuring the differential on loading on each rail, they could detect shifted or off center loads. They also used some in Nebraska to study the effects of wind on trains and to try and validate blow over speeds, by comparing the differential in loading and comparing it to the wind speed and direction.
The UP has an ultrasonic wheel defect detector in N Platte. They run an inbound train through the detector and a sensor "pings' each wheel, if the wheel "rings" its good, if it "thuds" its got a crack in it. Its affectionately known as a the "crack house". Then the UP benchmarked NASCAR pit crews and when they identify a broken wheel, a crew goes out into the yard and can jack up the car, replace the wheel and put the car back together in less than 20 min while its still coupled in the train.
Several railroads have vertical and horizontal loading accelerometers on engines and as they travel over any railroad they measure the line and surface of the track and download it to the AAR who distributes it to the appropriate railroad. Then neat thing about them compared to a track geometry car is that they load the track structure so they get a "better" measurement under actual conditions. Similarly they have several boxcars that have a huge concrete slab inside the car and telemetry devices on the car and trucks to measure track geometry, also under load, thanks to the concrete slab. One study I did right before I left was to see how many track defects were being reported as a result of those engines.
They also have a new track measurement device that puts a horizontal pressure on the rail as the car moves across the railroad and it measures the deflections. That's used to detect bad ties and spikes (rail fastening systems)
