If a train is stopped on the desired section when you first turn the system "on" how does it know to report the section is occupied?
The camera-based lane occupancy sensors for traffic signal control at intersections work at night though I don't know if they use the reference based image method. Since they must deal with snow on the road I'm thinking not. It too has the advantage of not having to dig up the road to install the sensor loop. I figure they must use a similar method of polygons to define traffic lanes and additional tricks such as counting the number of vehicles queued.
