Pennsylvania Power & Light Company. Predecessor and subsidiary companies. Local transit companies.

The development of electric distribution systems and workable traction motors led to widespread construction of trolley networks in the 1890s. Many systems began as electrifications of the horse car lines that had appeared in major cities starting in the 1850s and spread to county seats and other large rural towns over the next twenty years. Electric traction made possible the construction of light interurban rail lines linking cities and their outlying villages. Such transit systems were cheaper to build and operate than steam railroads.

As traction systems were large consumers of electricity and required electric distribution networks along their lines, they were amalgamated with electric power companies at an early date. Ultimately, the large electric holding companies that emerged in the first two decades of the 20th century acquired near-monopolies of electric traction as well as electric power and distribution and sales within their respective territories.

Trolley and interurban systems peaked in the years before Wold War I, after which they were rendered increasingly non-competitive by rising labor costs. Interurban and rural routes were beginning to fail in the 1920s, and the Depression merely finished them off. In more densely populated districts, electric traction systems were gradually replaced by bus routes during the 1930s and 40s. With the exception of a few very large cities with heavy commuter traffic, most systems had been dismantled by the early 1950s.

The electric utilities generally set up motor bus affiliates for their transit systems during the 1920s and gradually substituted buses for their street car routes. However, many companies divested themselves of their transit systems once they ceased to be large users of electricity. Pennsylvania Power & Light disposed of its last transit companies in 1939. Those systems that survived were eventually acquired by public transit authorities in the 1960s and 70s.