Aiming an interrupter detector can sometimes be a problem,
especially with LEDs which can have a narrow beam. But this
problem can be overcome.
A somewhat thornier issue is how to scenically camouflage all
of the line-side light sources and light detectors. Some can be
hidden behind relay cabinets, bushes, sheds, signs, etc.
But after some number have been hidden, the layout might
become cartoonish for all of the clutter beside the track.
The problem is compounded if double or triple track has to be
detected separately. All of these limitations can be overcome
