US 340 originally followed Sandy Hook Road south and west from what is now Keep Tryst Road in Sandy Hook and paralleled the Potomac River west to Maryland Heights directly across the river from downtown Harpers Ferry. There, the U.S. highway crossed the river on a converted railroad bridge immediately upstream from the confluence of the Potomac and Shenandoah rivers and downstream from the two railroad bridges—one for CSX's Cumberland Subdivision on the north and the other for the Shenandoah Subdivision—that presently cross the river at the site. After the highway bridge was destroyed in the March 1936 flood, a wooden floor was placed on the Shenandoah Subdivision bridge for that bridge to temporarily serve both rail and automobile traffic. Later in 1936, Maryland and West Virginia acquired the right-of-way of the destroyed toll bridge owned by the Harpers Ferry and Potomac Bridge Company by eminent domain with an aim to build a new bridge at the site.