If you're trying to monitor railways for wear and tear, why not just use something that's already on the tracks all the time … trains? That's the idea behind the Tracksure system. Developed in a partnership between the UK's University of Huddersfield and engineering firm Siemens, it looks for trouble using an inexpensive sensor that can be easily added to locomotives.
The Tracksure sensor is designed to pick up on vibrations that are caused by empty spaces that have opened up between railway ties (aka sleepers) and the underlying ballast. These can cause problems ranging from rough rides all the way up to track breakage.
When such a void is detected, the sensor communicates the information to the locomotive's existing GSM-R cab radio system. These systems are currently present in all trains in the UK, along with many trains in other countries. From there, the GSM-R sends a repair alert to a central control center, with the geographical location of the fault.
Down the road, the sensor may also be able to detect things like corrugation of the track, or even problems with the train itself such as flat patches that develop on the wheels.
Source: University of Huddersfield