During the Federal Cavalry advance north from Fort Laramie in 1876 to attack the large Indian encampment on the Bighorn, the old Army Iron Bridge across the North Platte at Fort Laramie didn't look so nice and clean as most of the pictures of it have in travel guides of today, or as in Bridgehunters, but it probably looked like its photo shown at the website given below by Starley Talbott of Wyoming:
Note the longitudinal "running boards" in the picture. You probably won't see them at many "historic bridge sites" used as pedestrian bridges in today's world. This is the only picture of the Fort Laramie bridge, of many viewed, that has "running boards" on it, which it probably had during its entire useful service life.
I suspect that the Beale Wagon Road's six Iron Bridges in Indian Territory had "running boards," on them, also, because they were expected to be used by heavy-haul commercial and military wagons of the day (1860).