In the 1990s, the northern section of the Mon Line began to be used, together with the Port Perry Branch, as a high-clearance route for double-stack container trains.

[7][8] On August 5, 2018, a train running on the Mon Line derailed east of Pittsburgh's Station Square complex and blocked the tracks, forcing freight service to be suspended.

During cleanup and inspections of the area, the Mount Washington Transit Tunnel was closed and "T" trains were rerouted via the former Brown Line through Allentown.

A preliminary report by the Federal Railroad Administration's investigation team found that a fractured track caused the derailment.

Norfolk Southern filed a lawsuit in December 2018 seeking $1.1 million in reimbursements from the city for the incident, claiming that they had neglected to maintain the hillside.