Specifically deigned for use at grade crossings, using Opto-Sensors to detect the train. Output controls flasher, gates, bells, etc.
 
Single-direction grade crossing detector with alternating flasher ion one circuit board. Operates with any length train. Independent of track power. Use in any scales. Can power two 250 ma loads (five grain-of-wheat lamps or ten LEDs per side). 10-18V AC or DC input.