For those of us who are older, the RT13 bridge across the railroad tracks in North Salisbury is called the Overhead bridge. The northbound span of the bridge was built in 1930 as an outcome of a number of auto/train accidents at this intersection of RT13 and the railroad tracks. The State reason for building the bridge is referred to as the Maryland State Highway administration Grade elimination program, meaning they wanted to do away with at-grade railroad crossings. The bridge is a metal girder, two span bridge with an H-20 design. The southbound span was built in 1951.
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, when going uphill, 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 watching all those drivers going in reverse over hills and bridges created the expression don't know if he going or coming.