Media Relations Contact:
Morgan Lyons

February 12, 2002

Information on DART Light Rail

DART's Rail Cars Are Electric-powered Wonders

As customers ride DART's electric-powered light rail vehicles, they are riding the wave of the future, and traveling into the past as well.

Like the streetcars of yesterday, the new non-polluting rail cars are powered by electricity fed from overhead lines. But each DART light rail vehicle is a state-of-the-art example of modern rail technology. A "catenary system" of two electrical cables provides stable working voltage for all trains on the 20-mile start-up track.

DART opened its light rail system in June 1996 with a fleet of 40 cars and has added 55 more cars to the fleet to improve service and to accommodate the expansion of the system to Garland, Richardson and Plano.

What makes it run?
DART's 23-mile light rail system requires about 2.7 million kilowatt hours per month from TXU to feed into the 16 mainline substations -- big gray boxes measuring 12 feet wide, 40 feet long and 14 feet high located at intervals of 1.5 to 1.75 miles along the line. Two more substations will provide power along the 3.5-mile line between White Rock and LBJ/Skillman stations.

Inside the substations, more than 13,000 volts of AC electrical power is converted into 600 to 900 volts of DC energy required to run the trains. Two additional substations are located at DART's Service & Inspection Facility. The power distributed from each substation varies, depending on the number of trains in service and operating speed of rail traffic.

DART is unique in having the only variable voltage power distribution system in North America. Each substation is polled for energy usage and voltages are varied according to energy used and energy needed. An energy management system logs and predicts the amount of energy needed by the system based on usage history and predicted schedule. The energy management system's main purpose is to reduce energy costs while providing proper energy to the light rail vehicle. Not all substations have to be operational for the light rail system to work. In the event of loss of utility power to a substation, the system is designed to provide enough power to compensate.

Substation power flows into catenary lines hanging 20 feet above the tracks. "Catenary" is actually a geometric term that refers to the curve of the heavy top cable that hangs in a scalloped design from pole to pole on hinged cantilevers that extend out to the middle of the tracks. Distances between poles vary between 50 feet on curves and hills to 210 feet on straight stretches of track. The shorter the curve or the steeper the hill, the closer together the poles must be to maintain proper alignment between the contact wire and the track.

Thinner contact wire is stretched taut between one and four feet below the curved catenary wire and is connected to the cable above by hangers placed 20 to 25 feet apart, again depending on the length of the span between poles. On the top of each rail car is a "pantograph" -- a bar 78 inches wide with a carbon insert for conducting electricity. The pantograph picks up power from the contact wire as it moves along the track, and feeds it into the four 175-horsepower electric motors that drive the train. Each light rail car weighs 107,000 pounds and carries 160 passengers.

DART Light Rail Technical Information