Nashua - Merrimack - Bedford 13761
The identification, consideration, and analysis of roadway and bridge alternatives for this project was key to the process and objective decision making. Design alternatives were rigorously explored and evaluated throughout the Preliminary Design process that concluded in the Fall of 2018. Following the completion of the Environmental Study, a successful Public Hearing, and the Finding of Necessity by the Special Committee in May 2019, the Recommended Alternative was approved.
A complete description of all the alternatives evaluated can be found in the Environmental Study. The following is a summary of the major project elements and a description of the Recommended Alternative that was selected for each element.
Mainline Turnpike
The Turnpike mainline typical section, which currently provides two 12 -foot travel lanes with narrow shoulders, will change to three 12-foot travel lanes in each direction with wider shoulders on both the right and left sides of the roadway. The box beam median guardrail will be replaced by a concrete median barrier between the northbound and southbound barrels. A major benefit of this project will be that, at the completion of construction, this roadway from Nashua to Manchester will be a uniform three-lane section, providing consistent driver expectation throughout this 12-mile length of highway.
Bridges over Pennichuck Brook
Two separate bridge structures carry the F.E.E.T. over the Pennichuck Brook (Bowers Pond) drinking water reservoir in Nashua and Merrimack. These structures are deteriorating, and they are not wide enough to accommodate the new third lane in each direction. The new bridge will be slightly longer than the existing bridges to minimize work in the reservoir and will accommodate the three travel lanes and full shoulders in each direction with a concrete median barrier between north and southbound traffic.
F.E.E.T. over Greeley Street
The Greeley Street Bridge in Merrimack does not require replacement or rehabilitation based on its geometry and condition. Instead, this project includes preservation elements to extend the life of the bridge. The primary elements of the construction include maintenance repairs and upgrades to the bridge rail, bridge deck patching, new membrane and pavement overlay, replacement of the existing median barrier with new concrete median barrier, reconstruction of the bridge joints, abutment repairs, and other minor repairs.
Naticook Brook Culvert Replacement
Naticook Brook is carried by a 60-inch diameter reinforced concrete culvert which crosses under the F.E.E.T. just north of Exit 11 in Merrimack. Since the existing culvert does not meet current standards for hydraulic capacity it will be replaced with a 90-inch diameter culvert on a new alignment, which provides the most cost-effective feasible compromise between hydraulic and environmental needs.
Baboosic Lake Road over the F.E.E.T.
The existing bridge, located in Merrimack, was constructed in 1954 and is on the State’s Red List and is in need of repair or replacement. In addition, this four span structure is not long enough to accommodate the proposed third lane that is to be constructed on the Turnpike in each direction. Consequently, this bridge requires a complete replacement. The Recommended Alternative includes the construction of a temporary bridge, likely to the south of the existing bridge. Once the temporary bridge is in service, traffic will be diverted on to this structure while a new bridge is built along the same alignment as the existing bridge. The temporary bridge will then be removed, and the new bridge will serve traffic while completely spanning the widened Turnpike below.
Wire Road over the F.E.E.T.
The existing bridge, located in Merrimack, is in need of repair or replacement. This four span structure is not long enough to accommodate the proposed third lane that is to be constructed on the Turnpike in each direction. Consequently, this bridge requires a complete replacement. The Recommended Alternative is to construct a new bridge north of the existing bridge, utilizing the existing bridge to maintain traffic. Once the new bridge is in service, traffic will be diverted on to this structure while the existing structure is completely removed. The new bridge will serve traffic while completely spanning the widened Turnpike below.
Baboosic Brook Culvert
The existing culvert is a twin-cell reinforced concrete box culvert in fair condition. Both cells of the box culvert have a width of 15 feet and a height of 14-feet. This culvert does not meet current standards for hydraulic capacity. Therefore, replacement is required. The Recommended Alternative will construct a longer, single span bridge on the existing alignment. The elevation of the F.E.E.T. will be raised as needed.