SEPTA riders should be prepared for several notable service changes that start this weekend: New schedules are going into effect, and Route 15 trolleys will be replaced by buses for three months due to track-renewal work.

Here's what you need to know about what's happening on the public transit system:

Route 15 trolleys: Track replacement, 3 months of busing

Buses will replace trolleys along the entire Route 15 between Sunday and Sept. 17. Trolleys will resume operating between Frankford and Delaware Avenues and 63rd Street and Girard Avenue on Sept. 18, the transit agency said.

SEPTA is putting in new track to replace the deteriorated materials last replaced in the 1950s.

Motorists should also expect some travel disruptions during the track-renewal project. Inner lanes on Girard Avenue will be closed to all traffic in separate, multi-block construction areas, though the avenue will remain open for emergency vehicles and deliveries throughout the work. Drivers should expect lane shifts and follow posted detours.

Bus, trolley, subway lines: Summer schedules start

SEPTA adjusts schedules on some routes during the summer to reflect seasonal ridership changes.

This year's summer schedules go into effect Sunday or Monday, depending on route.

Some lines will see no changes. Most routes with new timetables have only minor adjustments.

Regional Rail: Late-night, weekend service changes

Various adjustments to late-night and weekend service on SEPTA's Regional Rail lines start on Monday. The changes affect trains that depart after 9 p.m. and are due to track-improvement work. The transit agency said the schedule changes are expected to last about 18 weeks.

The routes affected are the Airport, Lansdale/Doylestown, Media/Elwyn, Warminster and West Trenton lines.

Riders on those lines should expect delays and check the agency's website for specific changes.