This page shows a successful attempt to operate block occupancy detectors for DCC systems in a closely spaced group and with cabled wiring.
http://home.cogeco.ca/~rpaisley4/xDetGroup.html
This circuit senses the flow of current across the rails when a locomotive or resistance equipped wheel set is in the block. Whenever there is a large enough current flow the detector will produce an output indication. The circuit requires no adjustment and indicates the direction the train is traveling and can provide a steady state output for controlling block signals and interlocks.
http://home.cogeco.ca/~rpaisley4/BODGP.html
This page is about a block occupancy detector that uses optoisolators to electrically separate the track from the detector output. Three versions of the detector are shown: Basic, Time Delayed and Direction Indicating.
http://home.cogeco.ca/~rpaisley4/OptoBOD.html