The bridge is perhaps the highest elevation in Wicomico County. When the bridge was first built the early model cars had difficulty driving up the steep grade of the bridge. This was due to not only the lower powered engines and gear ratios of the time but because most cars had gravity feed gas tanks instead of fuel pumps. Typical of the era was the Ford Model T. It had a 10 gallon fuel tank mounted under the front seat and if the tank was low on fuel it would tilt in a direction so gravity could not make the fuel flow to the engine. So in the early days of the Overhead bridge drivers would turn around and back over the bridge allowing the fuel to run to the engine and the reverse gears of the Model T offered more power than the forward gears, by backing up, it functioned in the same way as today's front wheel drive vehicles - pull rather than push.
Perhaps all those drivers going in reverse over hills and bridges created the expression don't know if he going or coming.