found on http://mecanicien.tumblr.com
but credit for learning what a B17 was doing on a bridge goes to Bob, Vonredbeard.blogspot who somehow figured out the plane, the location, and what it was doing on the bridge! Thanks Bob!
B-17 44-83624 being delivered across the Mad River Bridge to the USAF Museum at Wright-Patterson AFB, OH. B-17 was being towed by an American Coleman Model G-40 all-weather towing tractor (USAF classification is MB-4) which can be removed in hot weather. Made from 1954 to at least the mid-1970s. (thanks to Steve!)