The bedstead truss design for bridges was always the cheapest style of pre-fab metal truss bridge one could purchase from the factories. The end pieces extend down to the creek bed and form the supports for the bridge, thus eliminating the need for building stone or concrete piers. I have found three of these style bridges in Atoka county, Oklahoma, and 2 of them are still in use.
Interesting information on the 'bedstead truss' bridge design. I never knew there was such a thing, and I don't think I have seen this type of bridge up here. And, the image you captured is great.
Yes, there were thousands and thousands of steel-truss bridges built in factories in the USA and shipped to final destinations for assembly. There were catalogs that states, counties and communities could order from. You could specify design and bridge length and capacity. Parts were built and shipped in by rail to nearest depot, then transported by wagon to the final location.
There are plenty of these bridges built in the first decade of the 20th century still standing and providing service to communities. Of course, those bridges that have wooden decks will have their decks replaced every decade or so.