Of historic interest is the Proposed Truss Bridge over the Thornton River near Sperryville, as laid out by the Virginia Department of Highways on November 19, 1928. Figures shown nearby include the overall design plan, plus enlargements of parts of that plan. These include: the title of the plan, a close up of the side view of the bridge, and a general note about the bridge. For the latter, of particular interest is the roadway being 24 feet wide, and the bridge having a capacity to handle two 15-ton trucks passing.
As built by the Roanoke Iron and Bridge Works in 1929, using steel from Bethlehem Steel, the bridge in Sperryville is technically called a “pony Warren truss bridge.” Pony is the name given to short bridges that have no top. Warren is the name of the bridge design patented in 1848 by Englishman James Warren (and Willoughby Theobald Monzani, who probably had too complicated a name to include in the name of a bridge type). Engineering-wise, a truss bridge is, essentially, a number of easily and ruggedly constructed triangles, designed to handle heavy loads for long periods of time by constantly transferring any moving weights on the bridge to the ground.
The interesting point of the Sperryville bridge of 1929 is that the roadbed passes through the bridge part way up from the bottom of the bridge and not along the bottom. The reason is that the Sperryville bridge of 1929 had no “rollers” at one end to compensate for the expansion and contraction of the bridge metal due to hot or cold weather. The expansion and contraction was shifted to the roadbed. This loosey-goosey approach was the source of the vibrations felt on the bridge.
VDOT’s plan for the new bridge (as shown in the photo below) is meant to emulate the look of the old bridge.