(click on images for larger view)
Bridge No. 560
• Routes 4 and 7 over Housatonic River
• Open-spandrel concrete arch
• Length: 8 spans, 674' overall, 184' maximum span length
• Built in 1930
• Connecticut Highway Department, engineers
Soaring high above the Housatonic valley, Bridge No. 560 is an impressive example of open-spandrel concrete arch construction. It superceded a wooden covered bridge (since washed away) that carried River Road across the Housatonic River at a much lower level. The use of large arches allowed the Highway Department to solve several problems at once. By spanning the entire valley, the project provided a wider, stronger crossing safe from flood waters. It also bypassed the built-up part of the village of Cornwall Bridge, eliminated a railroad grade crossing, and allowed for improved interchanges between local roads and the two state highways carried by the bridge.
Open-spandrel arches were ideally suited for situations like this one. For large bridges, they offered great savings in material over filled arches. And unlike deck trusses, they did not require high piers between the spans, since the arches themselves provided the rise. This is the largest of a half-dozen open-spandrel concrete-arch bridges built by the State Highway Department in the early 20th century.