I was once told, by an old friend who worked at Bombardier, about another solution for grades crossing activations that was tried overseas, that used of a radio signal emitted by the train approaching the signal, which is received by the signal, and activated, rather than using a fixed track circuit activation.

This reportedly had the advantage of using the Doppler effect to determine the speed of the approaching trains. Slow heavy freight trains would have a different Doppler wave compression approaching, than high speed passenger trains, and detecting that difference would allowed the lowering of the gates to be adjusted for that approach speed to the crossing.

I believe he told me they had tried this in Northern Sweden where they had a problem with mixed operations between very slow moving iron ore trains, and relatively high speed local and intercity passenger trains. Does anyone know about this?