Bypass highways may not be the most glamorous of engineering projects, but they do have a profound effect on communities. Since divided highways control foot and vehicular traffic, planners use them to expand or limit access as needed to enliven centers of interest or protect them from excess flow. This requires more components than most observers realize, as multiple sections must work together to achieve project goals. 3D modeling not only previews how the highway infrastructure will come together, but it also guides construction of the many parts.

The Route 85 Slingerlands Bypass Extension, near the town of Bethlehem, N.Y., is a good example. State and town planners wanted to improve vehicle capacity, relieve congestion, improve safety, and provide sufficient lane capacity to meet 20-year traffic projections. They also wanted to enhance current land use, provide for projected land use changes, and facilitate economic development while minimizing or mitigating environmental impacts and improving bicycle and pedestrian accommodations. All this was to be done while maintaining traffic during construction — 16,000 vehicles each day traveling about 60 mph.

“The location and the environmental constraints were the primary factors contributing to the complexity of this project,” said Jeffrey Pangburn, an associate and senior project manager at Creighton Manning Engineering (CME), the design engineers for the highway. “The newly constructed parts of the bypass were designed in a context-sensitive alignment to avoid and minimize impacts to ravines, wetlands, and historic properties.”

In all, the Slingerlands Bypass involved construction of 1.5 miles of new, four-lane divided highway and reconstruction of 1.75 miles of two-lane highway into four-lane divided highway. Also, an existing bridge was modified and widened, and three two-lane roundabouts were built. The project was not only successful, it was an award winner: CME took home the 2009 Transportation Project of the Year Award from the American Public Works Association and the 2009 Gold Award from the American Council of Engineering Companies.

Models were useful in most phases of the project, particularly environmental aspects, according to CME CADD Manager Karl Detrick. “The 3D model and the digital terrain models (DTMs) were instrumental in designing and constructing the project to minimize environmental impacts. For example, with the models we were able to compare several different alternative alignments during the design phase and find the best ways to avoid wetlands and historic properties.”

Model-based design tools were used to develop the roadway’s horizontal and vertical alignments to meet the following environmental goals:

• provide buffer between the roadway and historic properties;
• minimize the number of ravines crossed, thus diminishing the overall section footprint;
• minimize the visual impact on existing homes and businesses by depressing the roadway;
• minimize impact on wetlands, and mitigate impact with creation of new wetlands at a 2:1 ratio; and
• design new storm basins and native vegetation buffers to filter project runoff.

The N.Y. Route 85 Slingerlands Bypass Extension project involved reconstruction of 1.75 miles of roadway and new construction of 1.25 miles of roadway, including four roundabouts.

The New York State Department of Transportation (NYSDOT) had delayed the award of this contract by five months, so the contractor, Delaney Construction, was working under extreme time pressure from the moment it began. But time was saved during the construction phase by close collaboration with NYSDOT and the design engineers. Luckily, the bypass was named a NYSDOT pilot project — one of just three statewide in 2008 — for the integration of machine-control technology and Bentley’s Quantity Manager estimating software, which allowed CME to provide a complete DTM to grading contractors.

Quantity Manager was used to link the DTM from InRoads to the project’s pay items database. Contractors used the combined tools to layout and grade the project with stakeless technology while precisely monitoring quantities. This facilitated movement of more than 200,000 cubic meters of earth in a relatively short timeframe. Grading this way was more efficient and improved accuracy, resulting in a higher quality project. Quantity Manager reports were also a big help to state inspectors on the project.

The DTM-enabled construction process was even flexible enough to accommodate a late project addition. During construction, the developer of a new technology park proposed that a fourth roundabout be added in the middle of the bypass to provide access to the park. It made sense and fit the town’s business development goals, so NYSDOT was open to the idea. But a change order contract would have meant unacceptable delays.

Instead, the new work was undertaken simultaneously under a highway work permit. NYSDOT, CME, Delaney Construction, and the town of Bethlehem all worked together to execute the work permit, and the Slingerlands Bypass — even with the last-minute roundabout — opened to traffic on schedule. The level of cooperation was so extraordinary that team members were presented with an informal Partnering Award at the 2008 Associated General Contractors of America/NYSDOT Technical Conference.

The two-lane roundabouts reduce vehicle stopping and starting — and therefore reduce fuel consumption and emissions — improve safety, and reduce average commuter delays.

The four roundabouts built into the Slingerlands Bypass are not the awkward, traffic-slowing circles that many associate with the term. Modern two-lane roundabouts are a very useful tool for traffic engineers, and they have worked well with this project. Because they reduce stopping and starting, the roundabouts reduce fuel consumption and emissions, leading to cleaner air in the region. They are also more efficient: NYSDOT analysts said the average commuter delay per vehicle was reduced by seven to 15 minutes during peak hours.

Perhaps most importantly, the roundabouts are safer. Before the bypass work, the signalized intersections that were replaced by roundabouts had an accident rate significantly higher than similar intersections statewide. Accident rates have dropped, and state and federal research confirms that roundabouts reduce accident frequency and severity compared with intersections.

One of the new roundabouts in the Slingerlands Bypass is at Blessing Road, which created a gateway leading into Slingerlands Hamlet. The roundabout slowed traffic entering the hamlet. Together with a new pedestrian network (including a pedestrian bridge and a main bridge renovation that accommodates bicycling and pedestrians), a canoe launch, and a picnic area on the Normanskill Creek, the bypass has reduced the impact of heavy traffic on the surrounding community.

The bypass project has also facilitated sustainable development of a 1.4 million-square-foot mixed-use commercial space known as Vista Tech Park. This will make a substantial contribution to the town’s nonresidential tax base. And thanks to careful planning, these positive outcomes should last a long time. Projections call for an increase in traffic of as many as 25,000 daily users during the next 20 years. The new Slingerlands Bypass is ready to accommodate that increase and will still support community life when traffic reaches that level.

Angus W. Stocking, L.S., is a licensed land surveyor who writes about infrastructure projects around the world. He can be contacted at angusstocking@gmail.com.