The West Trenton Line connects Center City, Philadelphia with the West Trenton section of Ewing, New Jersey. Like all of the Reading Company's commuter lines, the West Trenton Line was electrified in the early 1930s and has a mix of at-grade and grade separated crossings. Electrified service to West Trenton was opened on July 26, 1931. The RDG planned to also electrify tracks between West Trenton and the CNJ Terminal in Jersey City for long-distance service, but had to drop plans for electrification outside of the commuter service area due to economic setbacks as a result of the Great Depression.
Currently, most weekday West Trenton trains continue through downtown to Philadelphia International Airport via the Airport Line. Prior to the abandonment of the R-designations on the regional rail system, inbound West Trenton line trains continued on to Elwyn.
On July 25, 2010 SEPTA renamed the service from the R3 West Trenton to simply the West Trenton Line as part of system-wide service change that drops the R-number naming and makes the Center City stations the terminus for all lines. This also ended the combined R3 West Trenton/R3 Elwyn service.