Anyone know what this is? I've seen these on some bridges here and there on back roads here
(https://i.imgur.com/fRYWwtW.jpg)
Pretty sure it's some sort of tag for every bridge in VA. (The old ones at least)
They are generically called "bridge plates", but VDOT calls them Bridge Date Plates. Some states call them Bridge Builder Plates. In Virginia, they are still required to be made of thick statuary bronze and a new bridge plate is required anytime a bridge is retrofitted or widened.
Historically, the engineers and bridge builders of the mid-19th Century needed to reach a larger marketplace and advertised heavily. The most effective form of advertising was the "bridge plate". As is often the case, there would be more than one bridge builder in a particular area and they would compete fiercely for business. The more profitable opportunities were further away from these areas and it was harder to "be at the right place at the right time". But the areas with the most bridge builders were also widely known to have the best maintained river crossings. As there was always a need for new and replacement bridges, it would be common for travellers to closely inspect the bridges along a particular route with respect to collecting information about the best structures. Keep in mind that these folks were using horses and/or carriages, as the automobile industry wouldn't arrive for at least another half century. This form of advertising moved from wooden structures -to- iron plate structures -to- cable suspension structures and steel truss structure.
In the railroad world, we also have similar "bridge plates" but there seems to be a different genesis here. As it was common for boilermakers to install manufacturer plates on stationery steam engines, the artifact became standard protocol for not only locomotives, but also for stone bridge structures and later steel bridge structures (but not on wooden trestles). In railway signalling, we would see similar manufacturer plates for unique electromechanical devices (some of which were essential for moveable bridges).
In the modern era, it was still common for bridge builders to install a "bridge plate" on poured concrete structures. But as the industry has migrated to precast AASHTO standard-length stringers, it is not very common to see a contractor want to add a Bridge Builder Plate to what is essentially plucked out of an erector set. State DOTs have also considered themselves to be "bridge builders", so nowadays it is more common to see a DOT "bridge plate" on every structure to allow inspectors to quickly identify the date of the most recent construction/refurbishment. But be assured, the more elegant and more complex bridge structures still get a Bridge Builder Plate whereby the specialty contractor proudly stamps their trademark on the monument.
Let me put my other hat on. The generic term "bridge plate" means a lot of different things. Several of those definitions are still related to bridges. During World War II, the Corps of Engineers (and similar Allied engineering forces) would install a plate at both ends of a bridge or pontoon structure with a series of numbers to identify the maximum vehicle weight and speeds. The term "bridge plate" is also used to identify flat steel plates that are used as gussets, beam supports, shims, stiffeners and bearing plates. Not to mention those other things, like this dohickey on a guitar. But perhaps most common usage is in public transit, where a removable "bridge plate" is utilized to allow wheelchair access from a platform to a vehicle. And guys like me had to write all of the monotonous rules about how to safely use them and how to properly store them.