The Lincoln Institute put out map that shows different US data. They have 3 for showing bridges: good, deficient and obsolete.
If anyone’s looking for something to map, getting out and mapping the obsolete bridges would be good. They’re likely to be gone sooner than later.
The handy map tool : https://placedatabase.policymap.com
This is an example of a deficient bridge by my grandmother’s farm. Yes, no guard rails and it’s wood. It was built in 1950. I’d guess the county would like to replace this one since it’s the one road serving the area. But who knows. There are something like a 1/8th of the households around there than when the bridge was built.