I believe you may be referring to the head on wreck at El Monte, where Earl Nall and his brakemen were killed. The indication was green, but they were actually lined into the siding, due to an error by the signal maintainer, who also didn't have permission from the dispatcher to be working on the signal, either, as I recall.

Earl saw he was lined in and stayed on the radio and horn warning the opposing crew, who barely escaped with their lives. The brakemen jumped, but at 65 mph., didn't make it.

It was, and still is, the worst accident I've ever seen for the damage done, both engine consists were complete scrap, piled about 3 stories high. It was an absolute miracle, and by an act of supreme sacrifice, that only those two men were killed.