If there were severe slippery conditions at that location on that day, then there could be mitigating circumstances, however, it is still the responsibility of the engineer. If the engineer had been advised prior to his arrival at that location, or if he should have been aware of slippery conditions at that location (if that stretch of track is always bad during leaf season) then he has no real mitigating circumstances as he was aware of the condition coming into it.
Having said that, there is much more involved here than just allowing your train to pass the signal. How fast was he going when he first applied the brake to stop at the signal? How far was he from the signal when he first applied the brake? Did he try to stop the train by placing the brakes in emergency? How severe were the slippery conditions? Did the wheel slide system on the train operate excessively or improperly? If the engineer ran right up on the signal at 20 or 15 mph (whatever the ASC allows if this is ASC territory) and then applied the brake at the last second, not allowing for the slippery conditions, then he is certainly guilty of, at least, very poor judgement. If, however, he was approaching the signal slowly and cautiously, trying to take into account the slippery conditions, and the wheel slide system on the train overacted, allowing too much brake effort to be released too often for too long a time, it may have been almost impossible for him to stop. I have had trains where I approached a station on almost level track, during leaf season, at 7 mph, intending to stop, and feeling the train slowing sufficiently to stop properly in the station. Just about the east end of the platform, the wheel slip on the 3 car train started overacting, and the train slid 10 cars past the five car platform. It would have gone farther had I not put in the train in emergency, which disables the wheel slide, although sliding wheels will not stop as well as turning wheels.
My point in all this? Yes the engineer is responsible for the safe operation of his train, but sometimes situations arise that prevent even the best of us from looking like some Joe Newkid running a train for the first time.
Proven Theory #2 - If you don't work for the railroad, you don't know more than the people who do, no matter how many years you've hung around the tracks, or how well you think you understand railroading.
Rest in peace Jtgshu.