All it would take is for a freight to break down, or hit a vehicle at a crossing, at a particularly bad location from a train scheduling standpoint, and then have that give you a domino effect of causing two or three other train crews to go "on the law", meaning that they were on duty for the maximum length of time allowed by federal law. If the railroad is unable to quickly get a relief crew to those trains because of where they "died", especially when it happens on a stretch of single track out in the boonies somewhere, the result is a scheduling disaster of major proportions. When that train crew "dies" under the hours of service law, the train has to stop, wherever it is, and stay that way until a relief crew arrives to take over operation of the train. Remember that when you have a single track, if the train on that section of track stops, ALL train traffic stops on both sides of that section. I don't know if that was the problem today, but a simple problem can snowball pretty easily given the right circumstances. Obviously they at least try to find a double-track section to stop at, and each crew knows when their time limit is, and they usually make sure the dispatcher also knows, but frequently they end up as the cork in the bottle.
