Sunday, July 05, 2009

What Did He Say?

I forget sometimes that words mean different things to different people. Take the last blog on the subject of automation. Note the comment and my return comment.

In my book, and I guess I'm getting too old, automation is anything where a mechanical or electronic system (or a combination of both) intervenes in a process that could be (or once was) done by human hand. We forget that there weren't always signals that detected an occupied block. Those signals that do were invented a century ago and were automation. Now a lot of people think that something is not automated unless it is run by a computer chip.

In the case of the DC Metro wreck, it may be interesting if the final determination is a failure in automation that had nothing to do with computers. But it just makes my point. As automation gets older, it needs maintenance to avoid failure. In most cases, automatic block signals or occupied block detection systems, were designed to fail safe. They did this in a way that assumed that a live engineer (motorman) was operating the train. The operator had certain options (not necessarily only two), in the event of a dark signal. Even those options were supposed to err on the side of safety.

Which brings the question: In the DC wreck, how was the software written to respond to an occupied block (I'm guessing binary zero) or an unoccupied block (binary one), or to the equivalent of a dark signal (maybe neither but probably should also be a zero)? Or did the computer itself have to take the equivalent of a visual position and translate it to digital? Or what?

I'm speculating, because I know nothing about the design of this system - absolutely nothing, binary zero. I do know this: In designing any system of automation, it is better to design the overall system from scratch than to try to wed it to something older, slower, or just not in step with current trends. My point again?

If we are going to spend money to design automated train control systems, especially in the case of dedicated HSR, but also for light rail and transit, we need to go whole hog, or future designers and engineers will be trying to do patches and upgrades that just won't be as safe.

©2009 - C. A. Turek - mistertrains@gmail.com
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