At first glance, it seems appealing to suggest additional wheelsets under a given railcar type. From the track’s viewpoint, and in a simplistic analysis, trading a particular car’s four-axles for the use of six should allow half again more car weight. This paper will examine efforts to test this concept over the past century. Indeed, the railway marketplace has investigated the three-axle truck in both the freight and passenger car arenas multiple times over the past century. Except in heavy-duty flatcars, the record shows that each implementation has proven to be only temporary.
In general, three-axle freight trucks were developed for use with steam locomotive tenders in the early 20th century. These designs were then adapted to other car types over several decades, involving thousands of individual cars. Today, three-axle trucks are nearly extinct. This paper will address the history and status of three-axle freight trucks (or bogies) as used in North American railcar operations. Various past 20th-century applications will be discussed. International efforts will be reviewed as well. The very limited and remaining current usage of three-axle trucks is also discussed.