The viability of utilizing railroad flatcars (RRFCs) as the superstructure for low-volume road bridges has been investigated in previous research. In this research, the RRFC bridge concept was expanded to investigate additional construction variables, methods to improve performance and reduce cost, as well as refining the previously developed design methodology. These objectives were accomplished by field testing two bridges - one in Buchanan County and one in Winnebago County, Iowa - and examining the data obtained from those tests. Both the Buchanan County Bridge (BCB3) and the Winnebago County Bridge (WCB2) were constructed using three 89-ft RRFCs; the railcars were "trimmed" to meet the span requirements of each site. The BCB3 was 26 ft - 5 1/2 in. wide with a single span of 66 ft - 2 in. The abutments were constructed with five steel piles embedded into the concrete caps; supports at both reinforced concrete abutments restricted only vertical movement. A bolted longitudinal connection was used to join adjacent RRFCs, and a gravel driving surface was added. The WCB2 was 27 ft - 0 in. wide with a main span length of 66 ft - 4 in. and 2 ft - 4 1/2 in. overhangs. The abutments consisted of six steel piles and steel caps with sheetpile backwalls at the end of the overhangs. Supports at the east abutment were welded, while those at the west abutment were restrained only in the vertical direction. Timber planks were added for additional transverse live load distribution, and a gravel diving surface was also installed. The BCB3 and WCB2 were instrumented with deflection and strain transducers and the data collected were used to analyze the bridges' behaviors. For the trucks used in the field tests, measured deflections and strains (stresses) were below AASHTO live load deflection and stress limitations. Since truck weights used in the field tests were below those of design trucks, the deflections and strains (stresses) were theoretically increased to reflect the increased weight. These values were slightly greater than AASHTO deflection and stress limitations. Results from this research verified that RRFC bridges are an economical bridge replacement on low-volume roads if they are correctly engineered.