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Cover Story - December 2004

Award of Merit - Highway

Route 31 Dualization

Highway construction and environmental friendliness may seem to be contradicting terms, but the Route 31 Dualization Section 6E/6F project in Raritan and Readington, N.J. offers an exception.

"They addressed floodplain issues at the same time as they were developing a highway," one judge said.

The goal of the $29 million project was to improve conditions of Route 31, a two-lane undivided north-south highway in Hunterdon County, N.J. It has daily traffic counts exceeding 33,000 vehicles and a 50 m.p.h. speed limit.


The project improved 2.3-mi. of roadway from River Road in Raritan Township south to Stanton Station Road in Readington Township. The program included widening the road, changing the roadway profile, installing concrete median barriers, and providing inner and outer paved shoulders. It also replaced two structurally deficient bridges and a culvert used for drainage and as a pedestrian underpass.

The southbound roadway runs parallel to land within the Hunterdon County Park System, which is primarily wooded or wetlands. At the northern point of the project, the roadway runs parallel to the south branch of the Raritan River. The northbound roadway runs parallel to a steep rock slope.

The roadway also meanders to avoid or minimize impacts to numerous environmental resources, including the historic Hoagland Brittin Farmstead, various sites at Rowland's Mills, and park system hiking trails. The design and construction phase included archeological data recovery at the Rowland's Mills site to avoid impact to historic elements. The phase also involved a local education outreach program.

Once work commenced, the team took on several big tasks, including replacing the culvert that provided a pedestrian crossing of Route 31 for the Irvington School District Outdoor Education Center. In its place, the team built a 130-ft.-long lighted pedestrian underpass compliant with the Americans with Disabilities act.

The team also built three retaining walls to reduce the required embankment within the existing floodplain and wetland along the southbound roadway. The walls also limited the need to excavate into the rock slope along the northbound roadway.

One was a 2,200-ft.-long by 15-ft.-high median retaining wall to accommodate the split northbound-southbound profile. A second was 210-ft.-long along a bend in the Raritan River. Since shallow rock prevented drive sheeting, the team used a porta-dam system during construction to keep debris out of the river and protect the habitat from exposure to toxins released through concrete curing.

The walls didn't eliminate all need for excavation, however. The rock work was a big challenge, including one phase along the northbound side where a discontinuity in the underlying rock resulted in a slope failure during construction. The team halted work and shifted gears to explore other solutions, which entailed getting additional right of way to re-grade to flatter, more stable slope.

"They were very sensitive to the environment and to the landscape," one judge said.

Another big job was replacing the two bridges, one a 165-ft. span over Conrail railroad tracks and the other a 275-ft. long curved girder bridge over the river's south branch.

The retaining walls, bridge piers, and wingwalls have concrete tinting and ashler stone finishing treatment to enhance their appearance and integrate them into the surrounding environment. The design of the bridge parapets mimics the historic balustrades of the original spans.

The project also met the specialized needs of the greater community, including a request from the New Jersey Division of Fish, Game and Wildlife to maintain a pathway and leave adequate headroom for hikers and equestrian riders at the abutment and underclearance for the Raritan River bridge. The project team also coordinated with the state Department of Transportation's Bureau of Landscape and Urban Design to ensure that concrete tinting blended with native rock in the area.

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