Review of the AC Overhead Wires, the DC Third Rail and the DC Fourth Rail Transit Lines: Issues and Challenges

This paper focuses on transits available around the world. AC voltage transits and DC voltage transit are reviewed and compared. Emphasis is given to differences, advantages and disadvantages of voltage supplies and traction types. First, differences between bus rapid transit (BRT), metro, light rail transit (LRT) and light metro are covered, with special attention to statistical of annual passengers per year, an attribute that defines the type of railway transit. Mention is also made to the history of DC and AC overhead wires, other traction preferences for metro transit and highlighted differences between the third rail and fourth rail traction. Malaysian transit systems are then discussed, with special attention to LRT Kelana Jaya line, world's third DC transit that employs the fourth rail traction. The discussion have produced relevant statistical data that this paper is in part aimed at summarizing and at comparing with what accomplished on the same subject within the third rail traction framework. The increased in LRT Kelana Jaya line annual passengers per year is a proof of success for the fourth rail technology.