Service began in 1975 when the Port Authority assumed ownership of the Pittsburgh–McKeesport–Versailles commuter trains operated by the Baltimore and Ohio Railroad (B&O) with the support of PennDOT.

In the early 1970s, the Port Authority (PAT) – which had controlled all bus and streetcar service in Allegheny County since 1964 – had negotiated with the B&O and Pittsburgh and Lake Erie Railroad (P&LE), the last two private sector commuter operators in the region, about the possibility of expanded rail service.

Neither the B&O nor the P&LE showed much interest in expanded service, citing existing operating losses and declining patronage.

The B&O trains made the run from McKeesport to Pittsburgh in 25 minutes, twice as fast as comparable bus service.

Among the strongest supporters in the local government were then-mayor Peter F. Flaherty and County Commissioner William Hunt.

The capital costs would be split between the federal government, the state of Pennsylvania, and the county, and would include the purchase of two locomotives and nine coaches.

[3] A proposal by Hunt to extend service further to Elizabeth was unsuccessful: the route was owned by the P&LE, which requested $500,000 to rehabilitate the line.

[5] In 1978, PAT renewed its agreement with the B&O, and was finally able to secure the capital funding for the new equipment plus a new intermodal transportation center in McKeesport.

In a nod to railroad tradition, the Port Authority assigned names to the trains: PATrain, Early Bird, Pittsburgher, Golden Triangle, Shopper, Mid Day, Mon Valley, McKeesporter, and Youghiogheny.

PAT's operations director cited multiple factors, including fare increases, van pools, and a generally poor economic situation in the Monongahela Valley.

Finally, trains continued running west along the river to reach the B&O's Grant Street Station in downtown Pittsburgh.