The Delaware Valley Regional Planning Commission (DVRPC) has released a design guide for modernizing the Philadelphia-area trolley system.

Operated by the Southeastern Pennsylvania Transportation Authority (SEPTA), the trolley system serves nearly 100,000 people on weekdays. However, the 36-year-old trolley vehicles are nearing the end of their useful life and cause expensive stresses on the system, according to the guide.

To maintain service, SEPTA plans to pursue an estimated $1 billion plan to replace the vehicles and overhaul the entire trolley system. The modernization plan would include lower vehicle floors, ramps for accessible boarding, more seating capacity and additional doors.

“Trolley modernization’s most prominent streetscape impact will be at stations, where curb extensions are needed to make the system accessible,” DVRPC officials wrote in the guide.

SEPTA and its partner agencies should develop strategies to balance the safety and mobility of pedestrians, bicycles, drivers and transit riders, according to the guide’s recommendations. In addition, the guide suggests creating a coordinated, realistic plan to roll out modern stations.

The guide is intended to serve as a reference for planners, engineers and community members to understand the goals behind modernizing trolley corridors in the city.