Triple-digit temperatures Thursday could mean a slower commute for regional-rail and trolley passengers, SEPTA officials said Wednesday night.

Reducing speeds is a safety measure that the transit agency has to take when temperatures rise above 90 degrees, because overhead power lines typically droop in the heat and stiffen in cold weather, said Heather Redfern, a SEPTA spokeswoman.

"You certainly have to be careful using the equipment in the extreme temperatures to make sure you're not going too fast for what the wires can handle," she said.

"For the morning rush, it shouldn't be an issue, but if the temperature rises during the day some speed restrictions could be placed on the regional rail."

Redfern said that maximum speeds will likely be reduced to 30 miles-per-hour on the route 101 trolley, with service between the 69th Street Transportation Center and Media, and the route 102 trolley with service between the 69th Street Transportation Center and Sharon Hill.

She said that no specific rail lines have been more problematic than others in extreme weather, and officials will cover the service area looking for sagging lines and buckling tracks.

Redfern urged commuters to monitor the SEPTA website (www.septa.org), follow the agency on Twitter or call customer service at (215) 580-7800 for information on weather-related issues and to get real-time transit updates.