This rare Warren deck truss carries a railroad track over an unpaved road and the west fork of Crooked Creek in eastern Franklin Township. The bridge is built on a skew, being oriented on a northeast-southwest line while crossing an east-west road. The year 1903 is incised in one of the concrete piers, and presumably this date represents the bridge's erection date. The crossing was probably independently designed and built by the railroad, therefore no county records exist for the truss. Warren deck trusses are rare for highway bridges, although more common for railroad structures. Prior to 1940, numerous through and pony trusses were built on road and highways throughout Iowa. Deck trusses--in which the roadway is carried by the truss's upper chords--were built far less often, owing to the relatively flat nature of Iowa's waterways. "Only a few locations in the state will permit the use of this type of construction," the state highway commission stated in 1915. "This type of construction requires considerable head room about high water in order to allow its use." This uncommon truss type has suffered statewide attrition, until less than ten deck trusses are known to remain in Iowa. The CM&StP Railroad Underpass is distinguished as the oldest remaining deck truss in Iowa. It retains a high degree of both structural and historical integrity and thus is an important transportation-related resources [adapted from Zibell, Hess and Fraser 1992].
Ok I see. Perhaps someone could edit it a little to make it very clear it's from the point of view of roads
Since the essay was written from the perspective of roads, rather than railroads, and was hosted for the Iowa DOT, it's evident that they were speaking from the perspective of roads and road associating structures.
The essay isn't exactly true. There are deck truss bridges (on railroads) older than this one. This includes a CRIP crossing at Estherville (1894), the famous Kate Shelley High Bridge (1901) and the Fort Dodge High Bridge (1902)
Perhaps the better statement is deck truss bridges on OR over highways?