SEPTA riders should prepare for a number of changes to their trips this weekend. Here's what you need to know if you're getting around on public transit Saturday and Sunday.

New Regional Rail schedules: Perhaps the biggest change is that new schedules on most Regional Rail lines go into effect Sunday. The new  schedules are part of the beleaguered transit agency's effort to improve rail service after a rough year plagued by repairs, delays and overcrowding.

Schedules changes include adjustments to weekday train times, service to and from the Glenside Combined and Warminster stations on the Airport Line and new morning service to Center City from Warminster on the Warminster Line.

Trolley tunnel closure: The trolley tunnel in Center City will be closed from 5 a.m. Sunday until 5 a.m. Monday for construction work. Trolley service on Routes 11, 13, 34 and 36 will start and end at 40th and Market Streets; Route 10 trolleys will start and finish at 40th and Filbert Streets. All trolley riders should use the Market-Frankford Line for trips between 40th Street and Center City. Regular trolley service resumes at 5 a.m. Monday.

Airport Line shuttle buses: Shuttle buses will replace three early-morning Airport Line trains at the Glenside, Jenkintown-Wyncote, Elkins Park and Melrose Park stations on Saturday and Sunday. The buses will depart from those stations 16 minutes earlier than the regular train times and take passengers to the Fern Rock Transportation Center, where riders can transfer to trains. The rest of the Regional Rail line will operate normally.

Extra buses for holiday shoppers: Extra service, mostly to accommodate late-night shoppers leaving suburban malls, is in place on some bus routes throughout December, including this weekend.