The West Trenton Line is a SEPTA Regional Rail service connecting Center City Philadelphia to the West Trenton section of Ewing Township, New Jersey.

At Bethayres, it crosses the Pennypack Trail that runs along the former Philadelphia, Newtown and New York Railroad, which once connected with the Fox Chase Line.

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.

The line north of the split at Jenkintown was originally built as the National Railway project, opened on May 1, 1876, to provide an alternate to the United New Jersey Railroad and Canal Companies' monopoly over Philadelphia-New York City travel.

In addition to the Reading Company, which leased the North Pennsylvania Railroad in 1879, the Baltimore and Ohio Railroad also used the line for passenger and freight service to New York City, including its famed Royal Blue service.

[4] Beginning in 1984 the route was designated R1 West Trenton as part of SEPTA's diametrical reorganization of its lines.