SEPTA is anticipating that the delays that plagued Regional Rail on Thursday morning will be resolved by the evening commute.

A root cause of Thursday's problems should be familiar to regular Regional Rail riders: the vulnerability of power lines to weather extremes. Many of the lines on SEPTA's network are edging toward their 100th birthday. Whether it's bitter cold or a summer heat wave, temperature shifts cause the old overhead wires that carry power for the trains, called catenary wires, to expand or contract. Sometimes the wires break, and that's what happened late Wednesday when catenary at University City station cracked. Repairs extended into Thursday morning's commute.

In a problem unrelated to the wires in University City, a Chestnut Hill East train had an issue with its pantograph, the device that connects the train and the overhead lines. That damaged wires on the line between Wayne Junction and 16th Street, leading to more delays. Again, cold weather and old catenary appear to have been the culprits for the failure on that line, which suspended service on the Manayunk/Norristown and Chestnut Hill East lines Thursday morning. Repairs that kept the Chestnut Hill East Line suspended through much of Thursday were finished about 3 p.m.

SEPTA has been working on updating its power lines since 2000, and the wires in University City are among those prioritized for replacement. Of the 262 miles of catenary on the Regional Rail system, about 202 miles have been modernized.