> The Kansas Pacific only has ABS signals at its sidings, with dispatcher controlled interlocking (thus the (M) on the timetable page) at each siding switch.

By being dispatcher controlled, stricktly speaking these were not "ABS signals". As I recall, there were distant signals on the single track ahead of them, and this lead to a following train, which had been flagged out of a siding on a red controlled signal, misintepreting a yellow distant indication as an OK to increase to max speed, which isn't permitted by the rules. The result was a rear-end collision just before the siding switch at the next siding.