Stray current leakage and the corrosion caused by direct current (DC) traction power systems have been an ongoing issue especially in slab/embedded tracks. These tracks typically run through urban traffic areas, city centers, tunnels, and between the utility lines that require the rail to be continuously isolated to provide adequate track-to-earth resistance. Ballasted and direct fixation tracks provide much better track-to-earth resistance when equipped with isolation pads under the rail and exhibit higher stray current protection.
Various isolation techniques have been implemented by the DC powered rail transit agencies for the control of track-to-earth resistance in embedded tracks including the use of rail boot. In the last two decades, the practice of rail boot usage has seen a significant increase by transit agencies in the United States for controlling the leakage of current in embedded track sections. However, experience has shown that the rail boot alone cannot always control the stray current leakage and that it is important to supplement the rail boot with additional stray current collection and mitigation techniques. These methods thereby reduce the stray current corrosion by using various combinations of mitigation and collection techniques including, but not limited to, the use of elastomeric grout, insulated rail fasteners, embedding rail in troughs, providing current collection mats, and collector cables.
This paper presents and reviews different isolation and/or current collection methods that are presently in use to supplement the rail boot. These current isolation and/or collection methods when implemented together with the rail boot have significantly reduced stray current related problems, including: signal failures, controlling rail-to-earth voltages, minimizing recurring cost of repairs, and the damage to the public infrastructure. Additionally this paper provides general recommendations on the maintenance of the embedded tracks to avoid associated system problems.