That's more than likely kudzu on the bridge. When in bloom, it has little pink/purple flowers that smell sweet (sickeningly sweet).
They put a bunch around the mountains back in the 1930-40's trying to help fight erosion. It may have helped with erosion, but it liked the environment so much that it grew like a cancer. Many places in Appalachia are practically smothered by it today. My family has a cemetery in Loyall (a mile-or-so downstream from this bridge) and the only time you can get to it is when the kudzu has died down in winter.
It can be used for fiber. One of its medicinal properties has to do with alcoholism. Purportedly, if you use it for an herbal remedy, alcoholics will still drink, but be satisfied (therefore drink less alcohol) sooner. I've tried it and it kinda works. I just don't want it around my area as that would cause a disaster in regard to local farming.
Almost looks more like a trellis than a bridge, with all the plants climbing or growing through it. Does it bloom in spring?
This one needs a little TLC!