At the edge of built-up neighborhoods, the tracks of many trolley lines left the streets and traveled along a private right-of-way to reach their destinations in the suburbs and nearby towns. The necessity of maintaining these “open tracks” brought about the need for cars such as M551.

Dump car M551 is one of six such cars built for the Pittsburgh Railways Company in 1922 by the Differential Steel Car Company of Findlay, Ohio. When purchased, it became part of a fleet of eleven side dump cars owned by PRCo, and it represents one of the most common types of work cars used by streetcar companies in North America.

For Pittsburgh Railways, the side dump car was a natural because the topography of the Steel City provided many instances where embankments along hillsides and streams often required filling-in after landslides or washouts. This need, coupled with the task of removing cinders from the main power station on Brunot’s Island provided these rugged cars with plenty of work for many years.

Over-the-road trucks ultimately replaced dump cars. By the early 1960s, maintenance of just a few isolated areas along the Library and Drake lines had reduced the need for dump cars to just one. In 1977, Port Authority Transit shop crews rebuilt M551 with new cab ends. The car was ultimately retired in 1984 when new equipment obtained for the light rail system rendered it surplus.

Today, M551 performs the work it was designed to do at the museum, delivering ballast to track work areas and filling washout areas on our line, most recently after Hurricane Ivan washed out parts of the roadbed in September 2004.