BART

BART, or the Bay Area Rapid Transit System, is a cutting-edge-at-the-time commuter lightrail and subway in the California Bay Area. BART started operation in 1972 and is still running today, forming the backbone of public transit for San Francisco and much of the bay area. BART was one of the first transit systems to pursue a high degree of automatic train control, and was generally ambitious in its scale and technical sophistication. Now, though, over 40 years after the system was built, the rough edges on the design are only too apparent. This makes BART a great case study on transit systems and lightrail technology.

Wikipedia has thorough information on BART. Here, I attempt to add some details which I am not able to document to such a level as to add them to the Wikipedia article itself. Another good source of technical information is a report from PG&E. There are also a lot of odd details on the BART system's own "facts" page.

The remainder of this page is not well-organized yet, as it consists of scattered notes I've come across.

The prime mover on any BART car is four 150hp electric motors. This is either a DC motor or an induction motor on retrofitted A and B cars. These run directly off the 1kv DC third-rail supply, along with the electric heater elements. Everything else runs off of 208vac or 36.5vdc, mostly some fans, pumps, and of course the lights.

There is a released presentation on control modernization. There is also information in an old Univ. Santa Clara engineering case study. Also see an FTA report which is very long but has a case study on BART.

BART is primarily controlled by the Integrated Control System (ICS), based on track circuit communication. ACS is a speed-authority system in which each train is authorized to a specific speed value of 80, 70, 50, 36, 27, 18, 6, or 0 mph. Obviously, the commanded speed in the block before an occupied block must be 0 to avoid collision. Elsewhere, the speed is limited by either a design speed limit or the distance to the next occupied block. Blocks are as short as 70 feet, but generally must be long enough to allow a train to stop within their length. The BART track circuits run at an abnormally low voltage, which leads to issues when there is any corrosion on tracks. The track circuit is modulated at audio frequencies for control signals, exact range unclear.

There is also a “backup” train protection system called SORS, or Sequential Occupancy Release System. It works by detecting when the lead car has entered a block, and then releasing that block when the lead car is detected in another block that is a distance greater than the length of the train farther ahead. This means that missed detections result in a block behind the train remaining in the occupied state, a 'fail-safe' condition that is cleared by the control center when necessary. SORS is 'non-vital' as a safety system.

The Advanced Automatic Train Control system was contracted by BART with Hughes Aircraft in 1998 to replace the BART train control system. This did not end well. As of 2003, this project was still in progress with some test trains equipped and a section of track set up with wayside equipment. However, this project seems to be a total failure and has never gone into revenue service. Had the project gone anywhere, it would have implemented a “moving block” system based on radio sensing of the exact position of each train.