Even after the end of the Great War the Hagerstown & Frederick Railway continued to see an increase in traffic. By the early 1920s the company was reporting peak traffic - one year reporting 3,800,000 tickets sold in the fiscal year which exceeded the combined fares for BOTH of Baltimore's streetcar systems. Families were riding to Braddock or Electric park, thousands upon thousands were flocking to the agricultural fairs along both cities' "Loop" lines.
Despite this, there would be no further expansion of the rail network.
By the time the Hagerstown and Frederick was reporting 3.8 million passengers, it also was reporting that 67% of the company revenue was being drawn from selling what originally had been excess electrical power to residents and businesses. Emory Coblentz's vision had paid off. Seeing that their company had become more of a utility than a railroad the corporate entity itself was renamed in 1922 to become the Potomac Public Service Company.
The next year another purchase brought a better name, and with the incorporation of Cumberland's Edison Electric Illuminating Company and the Cumberland Electric Street Railway. At the end of 1923 the Potomac Public Service Company was no more, renamed instead to The Potomac Edison Company.
Potomac Edison continued to use the Hagerstown and Frederick name for its railroad operations, as it also did for the Chambersburg, Greencastle & Waynesboro Railway which it had purchased as well. Seeing a future in non-rail mass transit Potomac Edison purchased several small bus companies to operate alongside a brand new long-distance bus subsidiary it had formed called the Blue Ridge Bus Company. Trolley service was soon supplimented with parallel buses offering a similar schedule and more stops.
In a final investment to the railway several surplus passenger-only coaches were purchased from the Columbia Railway Gas & Electric Company in South Carolina for use on the Hagerstown based branches. When the CG&W and Cumberland Street Railway were closed in the 1930s some of the trolleys used on those systems were incorporated into the H&F fleet as well.
By the time war was beginning in Europe, the H&F was on a decline. Hagerstown's city loop past the fairground had been replaced with a bus in 1929, the Shady Grove and Jefferson lines were closed by the mid 1930s and when the State of Maryland decided to realign the Baltimore National Pike over the mountains, the main line between Myersville and Funkstown was removed in 1938. By 1940 all that remained was Frederick to Myersville and Thurmont, and Hagerstown to Williamsport.