After World War II rations ended it was only a matter of time before the explosion of automobile usage and the post-war roads improvements began. Trolley ridership quickly declined and freight demands declined due to the lack of war traffic and the increase in truck use. Potomac Edison began expanding its bus services and investing in new facilities for their Blue Ridge Bus Company, going as far as removing all but one track in the Frederick Carbarn to convert its space into a bus garage while Hagerstown saw the construction of a state of the art maintenance facility and bus terminal.
On August 4, 1947, Washington County said goodbye to its last trolley service as the three remaining interurbans in that county, #168, #169 and #172, took dignitaries from the Square in Hagerstown to Williamsport where a line of buses brought the passengers back.
For the last seven years of operation only the Frederick to Thurmont line remained in operation, but even that came to a close being replaced by a bus the same morning as one final round trip on a rainy February 20, 1954.
Freight service continued, with the electric freight motors being replaced by two diesel locomotives in 1955. The company sold off the bus assets within the year and the Blue Ridge Bus Company became the eastern United States network for Greyhound. The Thurmont tracks were removed within a couple of years and in 1961 the last remaining sidings in Frederick were sold to the Pennsylvania Railroad so that Potomac Edison could focus solely on being an electric utility.