This document discusses stray current corrosion from DC transit systems like light rail. It defines stray current as current through unintended paths that can cause metal deterioration. DC systems operate at high voltages and currents that can discharge into the ground and cause corrosion. Proper design and maintenance of electrical isolation for the tracks, as well as bonding of rebar and cathodic protection of nearby structures, can help mitigate stray current damage. Regular testing of adjacent utilities is also important to monitor for dynamic stray current effects. Corrosion from stray current discharge costs an estimated $500 million annually.