The road and bridge contractor lobby has to keep up the fear mongering. I'm not sure how accurate this data is because at least 2 of the bridges on the most traveled list are currently being rehabilitated. At least we made a dent with a 8.5% decrease from 2015 to 2016.
Most of the SD bridges in Oklahoma are county (off system) bridges that probably see 30 vehicles a day. If they have a weight limit of less than 15 tons a school bus doesn't cross them. If they do it's on the driver, not the county.
If we really wanted to get rid of the bad county bridges the ridiculous environmental clearance process would be reformed and streamlined. As it is, we are at the mercy of the US Fish and Wildlife Service. They value mussels, beetles, bats, fish and (non-endangered) birds over humans.