HAY STREET BRIDGE REPLACEMENT
Newbury, Massachusetts
The Hay Street Bridge over the Little River in Newbury was constructed in 1946. In conjunction with the project, approximately 1600 feet of causeway was constructed on new alignment over coastal wetlands to eliminate a bad curve where the former roadway traversed a hillside on the northerly approach to the river. The existing bridge is a four-span cast in-place curved and superelevated concrete deck, supported on wooden piles. The bridge was determined to be both functionally and structurally obsolete in 2000, and C&C was engaged to design a total replacement.
The presence of coastal wetlands has proved to be a significant challenge in meeting the current design standards of the Massachusetts Highway Department (MHD). The standards would require raising the deck grade to provide proper clearance of the 100-year storm with a single span structure, as well as widening the deck to accommodate currently desired travel lane and shoulder widths. The need to install new guardrail conforming to MHD standards would also mean widening the causeway. Our preliminary design work showed that it would be impossible to meet these standards without encroaching on the coastal wetlands.
The wetlands are an extremely valuable resource. The Little River is one of several tributaries draining into Plumb Island Sound, a major spawning and feeding area for many species of birds and fish. Also, during the Public Hearing, a number of area residents expressed concerns regarding aesthetics of the project. Several conservation groups, including the Trustees of Reservations and the Audubon Society, own the lands surrounding the bridge.
To date, C&C has studied a number of alternatives to reduce the wetland encroachments. These include minimizing the guardrail lengths by adopting the 2002 AASHTO Roadside Design Guide in place of the more conservative MHD Highway Design Manual. The use of a lateral wing wall with bridge rail extended back along the sides of the causeway has also been investigated. At the time of this writing, the Department has taken our study under advisement. It is likely that additional compromises will have to be made in the current standards if the project is expected to totally avoid wetlands impacts.
