computer malfunction on bart and la subway

In a event of a computer failure on Bart and la subway controlling them will they stop?

rail10 wrote:In a event of a computer failure on Bart and la subway controlling them will they stop?

In general, yes, the systems are designed so that failure of the critical computer systems causes trains to stop. The trains (they have drivers, you know) can then proceed at low speed after contacting the dispatcher. This is pretty much standard.

Of course you can never make a system completely failsafe against all possible failure modes, but for the most part they fail safe under almost all conditions There was an infamous bug in the design of the systems used for BART and Washington Metro which could cause trains to accelerate and crash.... but BART fixed the problem back in the 1980s, before there were any crashes. WMATA in Washington didn't, and the result was the crash last year.

A long time ago I came across an article about a commuter agency's automatic train control system, and, if I am remembering correctly, it was specifically about BART's setup. Quick summary of the articles is that if there is a malfunction in the computers, it's handed off to the folks in the control center. Failing that, there is always an operator of every train, whom can stop or otherwise operate the train as necessary.

Now, as for the Red Line, and Purple(?) Line, I've ridden it, and on some more uncommon occasions I can swear it's being ran by the operators. I do know the cars are made for ATC, but on those days the consistency between runs is variable, trains arrive inconsistently between a minute early to two (sometimes three) minutes late, and starts and stops are varyingly smoother or abrupt. Either they are tweaking the ATC computers allot on those days, or the system is running with ATC off. Now I don't mind it, as long as they don't overshoot the platform at North Hollywood.

It is worth further noting, for those who don't know, that in most systems there is a separation between "safety-critical" computer systems and "non-safety-critical" computer systems for ATC. If the non-safety-critical systems break down, the safety-critical ones (automatic train stops for block occupancy violations) may continue to operate, with the rest in manual mode.

This split is not universal, but is preferred as it means there is less of the system requiring really high-quality verification.

Automatic Train Control and Positive Train Control are in use around the world, and use computers that malfunction just as easily as those in the USA. Yet trains around the world are running almost all the time.