>> As for ATS, when does this kick in?

It actually depends.

With the old fashioned ATS (track magnet at the signal), passing any restrictive signal would have "plugged him", unless an acknowledgement was performed; but not before it was passed. Presumably then, he would have already acknowledged a yellow before the station stop. Then, as he passed the red he would have been "plugged", again unless he acknowledged passing the red. The freight would have received no warning whatsoever, as he had already passed the last signal to the west.

With ATC, it depends on how the track circuit in approach to the red signal is configured. In the ordinary case, his speed would have been restricted as he approached the red. He could have willfully acted to proceed past the red, where he would have lost the track codes, causing an automatic brake application if no further action was taken, but nevertheless still in the way of the freight.

If configured with a high-def loop or similar device, as is common on modern rapid transit systems such as BART, an automatic application of the brakes would have brought him to a stop before he violated the red signal.

In either case, if the red was passed, the freight would have been instantly warned wherever it was, followed by an automatic brake application if no deliberate action was taken to forestall it.

It should be noted that no system of logic can be devised by man, regardless of the technology, that could have warned the freight until after the violation had already occurred. That is, unless you know of a technology capable of prescient clairvoyance. In this case, there was only about a minute between the violation and the accident - not much of a chance for any warning to have prevented the accident, but might of reduced its severity though.

Obviously, the system works well when protecting against rear-enders, but is somewhat limited in preventing violations from causing accidents near where tracks cross over or converge, such as at any "CP". At such a location, an accident can follow a violation within seconds, just the same as it can at a highway intersection.

The only hope then is to absolutely prevent all violations at "Absolute signals". That is where the high-def loop or similar device comes in. It is a physical device attached to the track in approach to a CP signal at braking distance from approach speed, which detects that an approaching train has reached the point where brakes must be applied prior to a red signal. This occupancy detection causes the track codes picked up by the train to be changed to the most restrictive "absolute stop" cab aspect, requiring and enforcing an immediate stop - before the violation occurs. To my knowledge, these are not that common on American railroads equipped with cab signals / ATC such as the NEC. But they are common on the more modern American rapid transit systems. With these, ATC is fully capable and complete - indeed, fully automatic operation is possible with them, and not possible without them.

For those with more interest in how these systems work, go to the Simons - Boardman website. they have a lot of railroad educational materials, some of which covers signal systems of all sorts. Also, Amazon often carries their books. A perusal of the website could be useful for any railroad interest, as their coverage is very broad.

Simmons - Boardman

OPB