Hill To Hill Bridge
Location: Route 378, Bethlehem, PA Waterway: Lehigh River (and Reading Railroad line); the bridge joins Bethlehem and South Bethlehem) Bridge features: 9 approaches, 11 abutments, 48 piers, 58 spans Year: 1924	Bridge Type: concrete arch bridge with two metal truss bridge sections

BRIDGE HISTORY

Planning for the Hill to Hill Bridge began with the free bridge movement of 1891. After many set backs and forty seven plans (as of 1919), work began on the bridge on August 1, 1921. High steel towers for pouring concrete were erected and two central concreting plants were also constructed. The work at the height of operations employed 350 men. During the summer of 1922, 1000 cubic yards of concrete were poured in a 24-hour day. The original bridge has nine approaches, eleven abutments, forty-eight piers, and fifty-eight spans. It was considered an engineering marvel when it was first constructed.

Later structural changes included a new span in 1965 to carry Route 412 over East Fourth Street and the Lehigh Street ramp was removed. In 1967, the Plaza in the center of the Hill to Hill Bridge was removed. In 1973, the Second Street ramp was closed to traffic as it was considered a traffic hazard. A major rehabilitation contract consisting of structural repairs, re-decking and resurfacing, curbside walls, drainage system improvements, painting of steel structures, and new traffic signals cost 8.6 million dollars; these repairs began in 1990.

BRIDGE STRUCTURES

The arch ring on this bridge is a single unit (solid, with no ribs) - termed an arch barrel. Reinforced concrete arch barrel spans are the major structural elements in this complicated bridge.		The bridge passes over the Lehigh Valley Railroad line today.
Simple columns suggest a classical architectural influence. This part of the bridge is where the Main Street approach joins Route 378.		This pier has the force of two arches (left and right) pressing in against it.
Here are bridge piers on the upstream side of the Lehigh River. They are shaped to protect the bridge from flood debris.		Here is the bearing seat of one of the metal truss sections of the bridge where it joins the cement structure.
An overall arch structure forms the top of the two truss structures.		Bridge trusses include diagonals which both include laced sides.
This view of lower chords and lower floor beams show how these structural elements form a rectangular pattern as seen from under the bridge.		The cantilevered sidewalk extends beyond the bridge trusses.