A growing problem with lateness on the Regional Rail lines in the last year is driving SEPTA to make big changes to its schedule, agency officials said Wednesday.

Those changes will begin Sunday throughout SEPTA's Regional Rail network, but the biggest adjustments will be on the Warminster and West Trenton Lines. Those lines will now terminate at 30th Street Station instead of at Philadelphia International Airport. There also will be a new, shortened Airport Line.

West Trenton Line trains were on time 76 percent of the time in October, officials said. The same month, the Warminster Line trains were on time 84 percent of the time, and Airport Line trains were on time 83 percent of the time. The changes are designed to bring the on-time rate on those lines up to SEPTA's standard of 92 percent.

For passengers on the Warminster and West Trenton Lines, the biggest change will be the need to transfer to reach University City or the airport, officials said. During off-peak hours, those two lines will no longer stop at Elkins Park, Melrose Park, and Wayne Junction.

Meanwhile, the Airport Line will run only from Temple University to the airport during peak hours, and from Jenkintown to the airport during off-peak hours. The net result of the alterations should keep the same number of trains, and in some cases more, serving all stations.

"These are three lines that should see an incredible on-time improvement," said Ronald Hopkins, SEPTA's chief operations officer.

Delays have numerous causes, but among them are two bottlenecks. Three lines use a route between Jenkintown and Wayne Junction that have only one track in each direction. Another bottleneck is near North Broad, where six lines use two tracks in each direction.

In addition, higher ridership creates delays. On average, 8,434 people use the Warminster Line and 12,711 use the West Trenton Line on a weekday. The ridership numbers mean a train's dwelling time - that is, time spent at a station - is growing. More passengers need more time to board.

SEPTA officials believe shortening routes and running express trains will resolve delays.

Implementing the new schedule has been laborious, Hopkins said, noting that it took months of analysis and computer modeling. And the process has not been without problems. A set of printed schedules distributed earlier this week had minor errors. They will have to be reprinted at a cost of $15,000 to $20,000, officials said.

SEPTA's website, www.septa.org, has new schedule details.

215-854-4587 @jasmlaughlin