The Overbrook Trolley Line was a set of railroad tracks that stretched between South Hills Junction and Castle Shannon.

The Overbrook line began in the early 1800s when the Pittsburgh Coal Company built railroads to move coal from mines in the Saw Mill Run Valley. Nearly 200 years later, abandoned mines were uncovered by surveyors doing advance work for the reconstruction of the line. The old mines caused subsidence.

Later in the 1800s, the Pittsburgh & Castle Shannon Railroad was formed and bought rights of way from the Pittsburgh Coal Company. The new railroad provided passenger service by day and transported coal by night.

An extension was added to Castle Shannon, marking the start of the Overbrook Trolley Line. For the first time, people who lived in the South Hills could easily commute into Pittsburgh. Commuters boarded at 14 passenger stations. They switched to inclines at Warrington Avenue and completed their trip to downtown by streetcars.

Pittsburgh Railways leased the line in the early 1900s, converted it to electric and made other upgrades to the service. A loop to Brookline was connected to the Overbrook line. Pittsburgh Railways’ interurban service to several stops in Washington County operated over the Overbrook Trolley Line tracks.

During the Great Depression in the 1930s, Pittsburgh Railways operated 90 trolley routes. Routes into Overbrook left downtown, crossed the Smithfield Street Bridge and East Carson Street, entered the Mount Washington Tunnel and stopped at the South Hills Junction, which provided a transfer point for a number of Pittsburgh Railways trolley lines. Departing South Hills Junction, the local line crossed Saw Mill Run Boulevard, passed through Overbrook and terminated at Castle Shannon.

The Port Authority Of Allegheny County acquired Pittsburgh Railways in the 1960s. A shift towards relying on buses rather than trolleys, which began years earlier, led to fewer trolley routes – only 16 remained by the late 1960s, the Shannon-Overbrook, Library and Drake lines among them.

During the 70s, planning began to convert the Overbrook Trolley line to modern light rail standards.

By the late 1980s, Pittsburgh’s streetcars were dated, unsafe and expensive to maintain. Trolley service was reduced further. Buses replaced trolleys on the Overbrook Line a few years later. It looked like the end of the line for the Overbrook Line.

New life was breathed into the Overbrook Line when ground was broken in 2000 to reconstruct the line from South Hills Junction through Overbrook to Castle Shannon. Today, the Silver Line and Blue Line operate on the Overbrook Trolley line tracks between South Hills Junction and Castle Shannon.