Abstract
As light rail transit (LRT) systems continue to develop throughout the United States, the newer extensions tend to have a significant proportion of their alignments physically separated from all street traffic. Where those sections are lengthy, this presents the potential opportunity to use third rail instead of overhead catenary, generally more costly, as a traction power distribution medium. The implications, both positive and negative, of site-selective use of third rail on future systems and extensions are explored. The designs and procedures that allow LRT cars and trains to draw power from both media alternately are discussed, and a method for accomplishing the transition when they remain in motion is described in some detail. Descriptions of some historical and contemporary practices related to the concept are also included. Encouragement is provided for considering the concept as a design alternative for new LRT lines and extensions of existing systems.
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