It connects Northwest Philadelphia, including the eponymous neighborhood of Chestnut Hill, West Mount Airy, and Germantown, to Center City.

Some stations are less than half a mile apart, a characteristic more commonly seen in an urban rapid transit system rather than a commuter rail line.

[citation needed] Between 1984–2010 the route was designated R8 Chestnut Hill West as part of SEPTA's diametrical reorganization of its lines.

Between June 26, 1987 – December 17, 1989 service terminated at Allen Lane with shuttle buses serving St. Martin's, Highland and Chestnut Hill West because of unsafe conditions on the Cresheim Valley bridge.

The original iron bridge dated to 1884 and was replaced with a $7.6 million steel structure financed by the Urban Mass Transportation Administration.