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From a plan to asphalt -- steps to build a road
by Iris Padgett, Wake Weekly Summer Intern
Long lines of traffic, dust blowing over cars, vehicles weaving among traffic cones and workers wearing neon orange.
They're only a portion of of what actually happens during a road construction project. Road planning The planning and designing process can take several years to complete. Then there's the physical construction, which depending on the size of the road, adds on another few years. The first stage of road-building is scoping out the area where the road might be located to determine which path would have the least impact environmentally, said Shannon Sweitzer, state roadway construction engineer. Planners take into consideration a road's cultural and financial impacts as well. Roads can mean more traffic through a town -- causing cultural changes and financial growth, he said. Only then, using a process called photogrammetry, do planners determine elevations and topography of the area using photos. When designers lay out the road plans, they have to determine horizontal and vertical curvature and meet design policies according to where the road will be built and the size of the road, Sweitzer said. He said differences in road design come with differences in climate and land formation. For example, he said, if it rains often in a particular area, the road must have an adequate slope so the water runs off. And, if it's often snowy in an area, bridges will have de-icing equipment built into them. If an area is mountainous, the roads must mold to the hills. If the ground is flat, hills must be made to provide adequate drainage systems, Sweitzer said. After the planning and designing is completed, workers can finally begin the physical construction of the road. Several groups of workers with different specialties are needed in this part of road-building. Some companies have their own specialists, some hire subcontractors, said Brian Harrington, project manager for Barnhill Contracting Company, the contractor for the first leg of the N.C. 98 Bypass construction. Subcontractors are often needed for the construction process. Subcontractors needed to construct the N.C. 98 Bypass specialize in bridge work, culvert installation, stabilization and paving, he said. Road construction First, trees are cleared from the future road's pathway. While removing trees, erosion control devices must be installed to keep the dirt from washing away. Harrington said erosion control can include silt fences, sediment basins or diversion ditches. These all help contain runoff from a cleared site. After clearing comes the moving and mounding of dirt to create even surfaces and places for bridges. The next step in the road-building process is rough grading, Harrington said. Rough grading evens the surface more, though not to a perfect level yet. If the road requires culverts, large concrete pipes in a box shape that divert streams from one side of a road to another, they are installed at this point in the process. After rough grading, storm pipes and drains are installed, as well as water and sewer items. Harrington said this can be one of the lengthiest parts of the process. Next, graders fine-grade the already rough graded soil. This is called the subgrade. In this process, workers start meticulously grading the road to match the levels called for by engineers. The soil is then stabilized to add strength and durability to the subgrade. Stabilization is done with lime or cement or both. An engineer takes samples of the soil and makes recommendations on how to stabilize it, depending on its characteristics. Fine-grading is done again after stabilization. Then, a stone base that can be like gravel is added -- an aggregate base course. If a curb or gutter is needed, it's placed after the aggregate base course. The aggregate base course is then fine-graded to meet the engineer's design. The next stage of the process is the most familiar part -- paving. Depending on projected traffic volumes and truck weights, as many as four layers of asphalt can be used. The first layers are poured, but pavers wait to put down the last layer. Before the last layer of asphalt, construction workers complete sidewalks, he said. Then the final surface is installed. The last part of the road-building process is putting down pavement markings and installing signs and lighting. After a road is finished, Sweitzer said some agencies, like the N.C. Department of Transportion, restore natural areas around the road when they are finished paving. "We want to make sure North Carolina is preserved," he said. "Of course, because we all live here." Construction challenges Harrington said many things can make the building process more complex. Excessive rain in 2002 and 2003 caused delays on the N.C. 98 Bypass. Dirt just can't be moved or compacted if it is saturated. Another problem Harrington has experienced lately is a concrete shortage. He said pavers couldn't get as much of the material from suppliers recently. But technological advances in the past few years have helped make obstacles easier to overcome. Over the past five or six years, Harrington said, engineers have developed a new asphalt design that is more-region-specific. The design allows for differences according to traffic volumes and temperatures. Any part of the process may be easy one day and hard the next; it just depends on the conditions, Harrington said. "(Building a road) requires planning, scheduling and coordination," he said, so when complications arise, they can be dealt with swiftly.
Last Updated On: August 5, 2004
Copyright 2004 The Wake Weekly