AC single rail track circuits are used in specific railroad applications where cost, traction return, and operating conditions make them suitable.
One major advantage is reduced cost. Since only one rail needs insulated rail joints, fewer insulated joints are required compared to an AC double rail track circuit.
Fewer insulated joints can reduce installation time, material cost, inspection needs, and maintenance work. This may be useful on long track sections where minimizing infrastructure cost is important.
AC single rail track circuits can also be useful in electrified territory. The continuous rail can serve as a return path for traction current and track circuit current, helping simplify the return current path.
However, AC single rail track circuits have limitations. Since only one rail is insulated and actively segmented for the track circuit, broken rail detection may be limited mainly to the insulated rail.
Because of this limitation, AC single rail track circuits must be applied carefully based on operating needs, safety requirements, traffic density, inspection practices, and the type of traction power used.