With trains operating at speeds of up to 125 miles per hour (201 km/h), it is the fastest commuter rail line in the United States.

Additionally, Amtrak operated a commuter service named the Chesapeake from Washington to Suburban Station in Philadelphia between 1978 and 1983.

Amtrak, which had acquired the right-of-way from Penn Central, took over operation of the former Pennsylvania Railroad commuter line, which was rebranded as AMDOT (Amtrak/Maryland Department of Transportation).

[4] The Amtrak Chesapeake was discontinued later in 1983 due to low ridership and redundancy with AMDOT; a year later, all commuter rail service in Maryland was merged under the MARC brand.

With frequent MARC and Amtrak service, the Washington-Baltimore section of the Northeast Corridor is one of the busiest rail lines in the United States.

Most electric and rush hour diesel trains are 6-8 cars long, and are primarily made up of Kawasaki bi-levels.

For the spring and summer months, weekend Penn Line trains also include a single-level Bike Car that is specially equipped to accommodate bicyclists.

As with the former Bike Cars, these services are first-come, first served with no additional charge, and the bicyclist must make sure to be able to access the platform of the station they desire.

Amtrak's Acela, Northeast Regional, and other long-distance trains share tracks along the whole of the Penn Line.

[11] In 2020, Delaware State Representative Edward Osienski and State Senator Stephanie Hansen cosponsored a resolution to the Delaware General Assembly that would add commuter rail service between Newark and Perryville, involving an extension of MARC service to connect with SEPTA at Newark.