The forty bridges in this thematic study are the best of their types which were still in use on the state and county road systems in Wyoming when the study was completed in 1982. Selected from a statewide survey of all functional vehicular trusses and arches using a specific evaluation criteria and methodology, most represent superlatives of their generic engineering types (i.e. truss configuration and connection types) while typifying bridgebuilding and transportation trends in the state. All were built in the first three decades of the twentieth century (1905-1935). Although bridges were put up during the earlier periods of overland wagon emigration, they had not begun to proliferate in the state of Wyoming until the early twentieth century with the emergence of the automobile as a principal form of transportation. All the listed bridges display a remarkable homogeneity of construction and operational histories. Generally, county-built trusses were contracted through competitive bidding among several Midwestern bridge erectors and built from standardized designs using prefabricated components. After creation of the Wyoming Highway Department in 1917, the role of the counties in truss bridge construction diminished. The later highway department bridges were typically designed from standard plans maintained by the department and built by local contractors from components fabricated in the same Midwestern foundries.
One feature that all steel truss bridges shared was their versatility. Quickly erected, they could also be dismantled and moved if necessary. Many county road bridges in Wyoming had begun service as railroad bridges, sold or given to the counties as obsolete structures. Similarly, early highway bridges which had become unsuitable to handle increasing volumes of traffic were sometimes replaced with new trusses, with the older bridges demoted to places along less traveled roads. After World War II, new trussbuilding was rare in Wyoming. Today trusses have been largely superseded by more sophisticated engineering designs and are seldom erected. The remaining highway and roadway truss bridges are remnants of past technologies, whose numbers are continually dwindling through attrition.