The S Bridge: Engineering Trick on the National Road
Ohio
Where the National Road crossed Salt Fork Creek at an angle, engineers in the eighteen twenties faced a geometric problem. A bridge perpendicular to the road would waste stone; one parallel to the creek would be too weak. Their solution was the S Bridge: a stone arch built perpendicular to the creek's flow, with curved approach walls that bent the road into an S-shape to meet it.
Travelers curved left, crossed the arch, then curved right and were back on the road. The result was structurally sound, economical, and elegant. Guernsey County, Ohio once held several of these S bridges where the National Road crossed its creeks at oblique angles.
This one at Salt Fork survives as one of the best-preserved on the entire road.
