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Re: TrainNews eBart: BART gauge origin?
Author: Fred
Date: 12-31-2013 - 20:17
Third rail is used on subways to keep the diameter of the hole as small as possible. BART uses a 14 foot diameter tunnel. For overhead wire the hole would have to be near 30 foot diameter. The cost of digging a subway is proportional to the cross section. Compare the area of a 14 foot hole with the area of a 30 foot hole.
BART uses the standard General Electric 1200 VDC third rail system. The voltage was reduced to 1000 volts to get regenerated power to flow to trains that could use it. Traffic is so heavy on BART now that the reduced voltage third rail is no longer needed and the third rail voltage today is 1200 VDC or higher depending on the load.
When Rohr got the contract to build the BART cars they subcontracted everything under the floor to Westinghouse Electric. Westinghouse selected hydraulic brakes to save weight and space. It has proven to be a good system. The enemy's of air brakes are leaks, moisture, and lack of lubrication. All of these are resolved with hydraulic brakes. Also the non compressible pressure medium, the oil, provides immediate feed back on pressure and volume, which works well with an electronic controlled system. BART is the largest rail user of hydraulic brakes in the world.
BART was built without signals because there was not supposed to be anybody in the cab to see them. The system was to run fully automatically. There was to be a train attendant, who was pictured in early promotional literature as walking through the train mixing with the passengers.
The BART cars were to be very light to save money. The structures were built to carry light weight cars and save on electric power. BART cars were to weigh 50,000 pounds each, but they came in at 59,000 and 57,000, A/B, and went up to about 65,000 pounds with fire hardening after the transbay tube fire. This was the reason for rerating the el structures. During the design phase everyone expected St Louis car to get the BART car contract. Roar was a surprise and the BART contract going to Rohr is probably what put St Louis out of business.
BART uses the standard General Electric 1200 VDC third rail system. The voltage was reduced to 1000 volts to get regenerated power to flow to trains that could use it. Traffic is so heavy on BART now that the reduced voltage third rail is no longer needed and the third rail voltage today is 1200 VDC or higher depending on the load.
When Rohr got the contract to build the BART cars they subcontracted everything under the floor to Westinghouse Electric. Westinghouse selected hydraulic brakes to save weight and space. It has proven to be a good system. The enemy's of air brakes are leaks, moisture, and lack of lubrication. All of these are resolved with hydraulic brakes. Also the non compressible pressure medium, the oil, provides immediate feed back on pressure and volume, which works well with an electronic controlled system. BART is the largest rail user of hydraulic brakes in the world.
BART was built without signals because there was not supposed to be anybody in the cab to see them. The system was to run fully automatically. There was to be a train attendant, who was pictured in early promotional literature as walking through the train mixing with the passengers.
The BART cars were to be very light to save money. The structures were built to carry light weight cars and save on electric power. BART cars were to weigh 50,000 pounds each, but they came in at 59,000 and 57,000, A/B, and went up to about 65,000 pounds with fire hardening after the transbay tube fire. This was the reason for rerating the el structures. During the design phase everyone expected St Louis car to get the BART car contract. Roar was a surprise and the BART contract going to Rohr is probably what put St Louis out of business.
