Stray Current Mitigation and Collection Techniques Adopted by a DC Transit Agency and Its Effectiveness in Controlling Stray Currents

Stray current leakage and the corrosion caused by direct current (dc) traction power systems has been found to be a concern in slab/embedded tracks. Embedded tracks typically run through dense traffic areas, urban commercial centers, inner city areas, tunnels, and tread between utility lines that require the rail to be continuously isolated. This isolation of the embedded tracks is necessary to provide adequate track to-earth resistance. Compared to embedded tracks, ballasted tracks have lower stray current leakage since the entire rail does not require continuous isolation from earth and separation is only needed at the contact points which are generally insulated. Stray currents can cause safety risks, thus stray current mitigation is an important element of the overall design of a rail transit system. This paper presents and evaluates the isolation and mitigation method(s), their effectiveness, and the existing testing and maintenance plan for the Houston Metropolitan Transit Authority of Harris County (METRO). The stray current isolation methods adopted by METRO, supplemented by an effective maintenance plan, have been successful in containing stray current, have eliminated loss of public infrastructure, and minimized recurring cost of repairs.