Granite State Replaces Worst Bridges

By Paul Fournier | September 28, 2010

Up in the north country, in New Hampshire's White Mountain National Forest, two of the state's lowest rated bridges are about to be replaced by safe, modern structures.

As part of that effort, R.M. Piper Inc. of Plymouth, N.H., is presently constructing temporary bypass bridges to divert traffic from the two structures that carry busy Route 302 over the state-owned Conway Scenic Line of the New Hampshire Railroad, and the Saco River, both located in the town of Bartlett.

Piper's $10.6-million contract with the New Hampshire Department of Transportation will replace the two bridges, which are on the state's "Red List" because of their low Federal Sufficiency Ratings (FSR). Prepared by NHDOT's Bureau of Bridge Design, the list includes 140 bridges requiring two inspections each year because of poor conditions, weight restrictions or type of construction. FSR values run from 0 to 100 — the lower the number the poorer the condition of the structure.

Both Bartlett bridges being replaced were built in the 1930s and are narrow and in very poor condition. So poor, in fact, that the bridge over the railroad track's 11.0 FSR places it among the 12 lowest ranked bridges in the state. And the structure spanning the Saco River has a lowly 29.1 FSR.

In addressing the status of New Hampshire's bridges, TRIP, a national non-profit transportation research group, released a report in March 2006 that evaluates the conditions of roads and bridges and assigns grades to traffic congestion and traffic safety.

According to the report, "Making the Grade in New Hampshire: An Analysis of the Ability of New Hampshire's Transportation System to Meet the State's Need for Safe and Efficient Mobility," 47 percent of state-maintained roads in New Hampshire are rated in poor or mediocre condition, earning the state a grade of D for its road conditions. The report also assigns a grade of D to bridge conditions in New Hampshire, noting that 32 percent of bridges in the state are rated as structurally deficient or functionally obsolete.

Specifically, 14 percent of bridges in New Hampshire are rated as structurally deficient, showing significant deterioration to decks and other major components. An additional 18 percent of the state's bridges are functionally obsolete. These bridges do not meet modern design standards or are no longer adequate for the volume of traffic that they carry.

Adding to the significance of the problem, the number of vehicles traveling over the state's roads and bridges is rising dramatically, and fatality rates from accidents are increasing accordingly. And the traffic fatality rate on New Hampshire's rural, non-interstate roads, such as Route 302, is more than twice as high as the fatality rate on all other roads in the state. Furthermore, while only 45 percent of travel takes place on New Hampshire's rural, non-interstate roads, 61 percent of fatalities occur on these roads.

In addition to the structural deficiencies of the two Bartlett bridges, Route 302 has sub-standard vertical alignment over the NH Railroad bridge and in the vicinity of West Side Road. What's more, the poor geometry of the West Side Road/Route 302 intersection yields insufficient sight distance for motorists looking eastbound onto Route 302, and this has led to a number of accidents in the area. Exacerbating the problem is a large swale, or depression, in the road between the two bridges where hazardous pooling of water occurs.

Designed to eliminate these issues, Piper's contract begins on Route 302 approximately 1,400 feet southwest of the West Side Road intersection and runs northeast 1.0 mile. Included in the contract are replacing both bridges, reconstructing Route 302 on an improved alignment, rehabilitating part of the existing roadway, and reconstructing about 1,500 feet of West Side Road. A new 5,000-foot section of water main with services is included in the contract to preclude having to tear up the newly reconstructed road in the future. That portion of contract costs for the water main installation is being paid for by the Lower Bartlett Water Precinct.

The NH Railroad temporary bridge will be in service for one construction season while the Saco River temporary bridge will be used for two construction seasons. Alternating one-way traffic controlled by flaggers will take place elsewhere on the project during off-peak hours for other construction activities. As a further contract requirement, traffic will not be maintained on the same unpaved section for more than three weeks.

Ground was broken for the Bartlett job in the first week of November 2006, according to Bruce Knox, P.E., Piper's field project manager. Garland Lumber Co. of Conway, N.H., was responsible for clearing the site. Piper crews are handling all of the site excavation and grading, while Wolcott Paving of Gilford, N.H., will install the bituminous concrete pavement. A limited amount of existing pavement cold planing will be accomplished by Pike Industries.

The two bridges have very different designs. The highway bridge over the Saco River will consist of steel girders topped with prestressed concrete deck panels and a thin cast-in-place concrete surface overlay. In contrast, the structure over the railroad will be a skewed, precast concrete arch.

Joseph P. Carrara & Sons of Middlebury, Vermont, is providing the precast deck panels, with Carolina Steel Corp. providing the structural steel and Coleman Concrete of Conway supplying all ready-mix concrete for the job.

For the bridge over the Railroad, Concrete Systems Inc. of Hudson, N.H., is designing and supplying a Con Span concrete arch bridge consisting of 29 arch frame units plus headwalls. The arches have a 36-foot clear span and a 10-foot rise. Butted together, with watertight barrier membranes at the joints, the arch frames produce a skewed bridge with a total length of 170 feet.

The entire project is scheduled for completion in October 2008.