AFAIK much/all of metal grating has been replaced with pavement. Metal grating is a bit dangerous but usually OK when riding in straight line. I'm more comfortable crossing bridges on a bike than a car. On a bike it's pretty impossible to topple over railing but in a truck it happens frequently & cars can actually climb overboard too. Anyway it blows that so many bridges don't allow bikes--adding a ped/bike apron would increase cost by what, 2%?

Drove down to Key West once & wondered about feasibility of cycling from Miami-Key West. Didn't see any bikes on the route (in contrast to large # of bikers in mainland South Florida) though it turns out to be legal.

Well DC doesn't have long bridges but bike tourists can rest assured that all the local bridges have nice bike paths where we can zoom past cars during rush hour.