Isaac Gardner was waiting for the train in Wellesley Square around 8:15 a.m. when the train arrived and then, just couldn't stop:
Might have been a slippery rail thing, but really wasn’t even close. Even loco at back went well past. First time I’ve seen that in a long time, and never by that much.
Once it did finally stop, the engineer put the train in reverse and backed up and picked up passengers - then slowly crept towards Boston.
MBTA Commuter Rail says that, yes, it was slippery rail - wet leaves and other wet stuff that causes the train equivalent of hydroplaning.
The next train, though, was delayed for another reason: A "rail defect" in Westborough.