Project Overviewbridge

The Sewalls Falls Road Bridge over the Merrimack River in the City of Concord is a 2-span steel Pratt Truss built in 1915 with a multi-span steel approach constructed on the westerly side in 1939 after the 1938 flood, to allow for floodwater storage. The bridge was designed by John William Storrs, a noted bridge designer and five-term Mayor of Concord and is the only one of Storrs’ designs remaining in Concord and only one of two 2-span steel Pratt Truss bridges remaining in the State of New Hampshire.  The bridge was evaluated according to the National Register of Historic Places criteria and based on this survey, the bridge is eligible for the National Register as an early example of a steel High Pratt Truss bridge.

This project was initiated in 1994 by the New Hampshire Department of Transportation (NHDOT).  In 1999, the Preliminary Engineering Services Phase of the project was begun.  Initial engineering evaluations focused on roadway alignment alternatives and associated impacts to cultural and natural resources.  Through the public engagement process and meetings with stakeholders, design alternatives also included means of preserving and rehabilitating the existing bridge to carry legal highway loads.  At the end of the NHDOT initiated preliminary Engineering, the Preferred Alternative was to rehabilitate the existing Sewalls Falls Road Bridge to carry one lane of northbound traffic and construct a new single lane, steel beam bridge just upstream of the existing bridge to carry a single lane of southbound traffic.  This was identified as the Proposed Action in the Final Environmental Study and Programmatic Section 4(f) Evaluation that was prepared by NHDOT in 2010 (2010 Studies).

At the conclusion of the Preliminary Engineering Phase, NHDOT turned the project over to the City of Concord to complete the final design and construction as a Municipally Managed Project under the Department’s Bridge Aid Program.  One of the first steps that the City undertook was to perform a detailed structural inspection and load rating analysis of the existing bridge to determine the extent of rehabilitation required.  The results of the inspection and load rating determined that, while the bridge could be rehabilitated to carry legal highway loads, the extent of rehabilitation was substantial and included either strengthening or replacing the majority of the structural members.  As a result of these findings, the City of Concord decided to reevaluate previously investigated alternatives to determine which alternative would best meet the near-term and long-term needs of the City and best serve the public safety.

To fairly evaluate the alternatives under consideration for the project, a formal Project Purpose and Need was developed.  The selection of a preferred alternative would be based on that alternative's ability to address the Purpose and Need, which is as follows:

Purpose and Need

The Purpose of this project is to address the current structural deficiencies and substandard roadway approach geometry associated with the existing Sewalls Falls Road Bridge, including the southern approach trestle and substructure units, in order to provide for the safe, sustainable, efficient, and cost effective multimodal movement of people and goods across the Merrimack River, while supporting the City of Concord’s short and long-term transportation, economic development, and regional emergency response needs.

The Need for the project is based on the following:

a) Sewalls Falls Road at its Merrimack River crossing is a critically important transportation link connecting an existing dense commercial/residential mixed-use corridor to the south and west to a proposed mixed-use development corridor with potential interstate access to the north and east side of Concord. Transportation system alternatives must balance the future needs of economic development in these areas with the protection of cultural and natural resources;
b) The structural deficiencies in the southern approach trestle, truss structure, and substructure units threaten access across the Merrimack River. A Federal Sufficiency Rating of zero (0) has limited its use as a one-lane bridge with a 3-ton load posting for passenger cars only, which precludes emergency response vehicles as well as all non-passenger car traffic from using the bridge;
c) The erodible nature of the riverbed and foundation design of the existing substructure units leave the bridge susceptible to scour during flood events;
d) The continuous maintenance needs of the bridge due to its critical condition are not sustainable with the City of Concord’s limited physical and financial resources;
e) The structural deficiencies and critical condition of the structures have resulted in a number of bridge closures, compromising the reliability of this critically important transportation link;
f) The narrow width and the limited load capacity of the existing bridge only accommodates a single lane of passenger car traffic resulting in operational inefficiencies to the traveling public such as delays for alternating one-way traffic as well as the need for non-passenger cars and those vehicles exceeding the 3-ton posting to seek alternate routes;
g) The narrow width and existing open steel grid decking of the truss structure do not meet current Americans with Disabilities Act (ADA) requirements and do not allow for safe passage of pedestrians and bicycles, severing the connectivity of the recreational trail system that exists on both sides of the bridge which is not consistent with the City of Concord’s Complete Streets Policy requirements;
h) The substandard horizontal and vertical roadway geometry on the east approach provides inadequate stopping sight distance which is not compliant with operational safety standards.

At the end of the Alternative Analysis, the City of Concord revised the Preferred Alternative to a replacement of the bridge over the Merrimack River at Sewalls Falls Road with a new two-lane bridge along the existing alignment replacing the existing structure.  New pier(s) and abutments will be constructed as the existing pier and abutments are in poor condition.