NH 1A over Hampton River Bridge Replacement

Seabrook, NH
New Hampshire DOT
Bridge ConstructionMarine Construction

Project Overview

This project will replace the State Red List bridge (Neil R. Underwood Bridge) that carries NH 1A (Ocean Boulevard) over the Hampton River at the inlet to Hampton Harbor.  The project limits begin on NH 1A in the Town of Seabrook approximately 1,500 feet south of the proposed bridge and continue northerly on NH 1A 3,900 feet across the bridge to a point approximately 100 feet south of the intersection with Ashworth Avenue in the Town of Hampton.

The existing bridge, constructed in 1949, is 1,193 feet between abutments and consists of 13-spans with a movable single-leaf bascule span in the center at the navigational channel.  The bridge width is 26 feet between curbs.  There is a single 4-foot-7-inch sidewalk along the east side.  The 150-foot-wide federal navigational channel is reduced to 40 feet as it passes beneath the movable bridge span.

The proposed bridge will be a fixed high-level steel girder structure on a new horizontally curved alignment west of the existing.  The bridge will consist of seven spans and have a length of 1,300 feet between abutments.  The bridge width will be 38 feet between curbs (two 11-foot travel lanes and 8-foot shoulders) and include two 6-foot sidewalks with overlooks at Piers 2 and 5.  The roadway shoulders will improve access for bicyclists and provide the ability to pass emergency vehicles through traffic queues.  The bridge will accommodate the full 150-foot-wide federal navigational channel with a vertical under clearance of approximately 48 feet measured from low steel to mean high water.  The improvements to the navigational channel will provide clearance for all regular waterway users, including US Army Corps of Engineers dredging equipment which is currently too large to transit the existing bridge for harbor channel dredging to the west.

Approach roadway improvements consist of full box reconstruction of NH 1A.  A pedestrian walkway will be constructed in front of the abutment beneath the north span (span 7) of the bridge which will connect Hampton Beach State Park to the Hampton State Pier property. Vehicular and pedestrian traffic will be maintained on the existing and/or proposed bridge and sidewalks as shown on the Plans and in accordance with the Traffic Control Plan.  Waterway traffic will be maintained within the existing federal navigational channel limits with normal operation of the existing movable bridge.  The existing bridge will be demolished upon completion of the proposed bridge replacement work.

Key Challenges Overcome: 

In water work is limited to time of year restrictions or working within cofferdams, which requires critical work to be potentially performed during non-ideal weather conditions.