Septa.org, 12/7/17:
A Message to Regional Rail Riders
Due to unseasonably late slippery rail conditions, several trains were operating with fewer cars and travel delays during the AM rush. We are doing everything possible to complete the repairs on the flat spots found on some car wheels and return them to service. These steps are necessary to ensure the safe operation of the system and the comfort of our riders, some of whom were inconvenienced by this morning's slippery rail conditions.