Diamond crossovers, where train tracks cross one another, are insulated from the signal circuits on the tracks that converge into the intersection. As insulators are moved away from the crossovers, as is the case for flange bearing approaches, the track circuit ‘dead zones’ can exceed a car length, preventing the signal system from verifying that the crossover region is clear.
Presence detection loops can be used, but they are mounted to the tops of ties – an area that is highly vulnerable to damage due to vandalism or when track and ballast work is performed.
The Island Radar has been successfully used by BNSF for detecting trains within the crossover structure. Two, and sometimes one radar mounted on 20-foot masts provides reliable train detection for the entire crossover region. The radar sensors’ output is easily interfaced to the signal system as a trap circuit release providing long lasting detection that is free of the consequences of tie-mounted presence detection loops.