Digital Terrain Models for Highway Construction

Digital Terrain Models for Highway Construction


Integrating Bentley Software with machine-control technology allowed Creighton Manning to expedite bypass extension project delivery

The New York State Department of Transportation (NYSDOT) retained Creighton Manning Engineering (CME), an engineering and surveying firm in New York, to design the $15.2-million Route 85 Slingerlands Bypass Extension project, which addressed capacity and service-level issues along a 3.25 mile highway section near Bethlehem. CME used Bentley’s InRoads software to expedite design and construction so that the bypass could open on schedule despite delays. For the Slingerlands Bypass, 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. In addition, this was to be done while maintaining traffic during construction— 16,000 vehicles each day travelling about 60 miles per hour. In all, the Slingerlands Bypass involved construction of 1.5 miles of new, four-lane divided highway and reconstruction of 1.75 miles of twolane highway into a four-lane divided highway.

3D modeling minimises environmental impacts
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 were instrumental in designing and constructing the project to minimise 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,” adds Detrick.

Model-based design tools in the InRoads Suite, Bentley’s software for civil engineering, were used to develop the roadway’s horizontal and vertical alignments to meet the following environmental goals:

  • Provide a buffer between the roadway and historic properties.
  • Minimise the number of ravines crossed, thus diminishing the overall section footprint.
  • Minimise the visual impact on existing homes and businesses by depressing the roadway.
  • Minimise impact on wetlands, and mitigate impact with the creation of new wetlands at a 2:1 ratio.

Pilot testing machine-control technology
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 construction began in February 2007. But time was saved during the construction phase through a close collaboration with NYSDOT and the design engineers, and the successful application of machinecontrol technology.

Slingerlands Bypass was named a NYSDOT pilot project — one of just three state-wide in 2008 — for the integration of machine-control technology and Bentley’s InRoads. The software allowed CME to provide a complete digital terrain model (DTM) to the grading contractors. Demonstrating a commitment to the technology and training required to meet project goals, CME collaborated with NYSDOT during the initial use of the Quantity Manager tools within InRoads and formulated suggestions as to how to best work with the tools.

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

Construction-stage design change
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. 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 in September 2008.

Energy, environment, and safety benefits
The four roundabouts built into the Slingerlands Bypass have eased congestion and reduced fuel consumption and emissions. They are also more efficient: NYSDOT analysts say the average commuter delay per vehicle has been reduced by seven to 15 minutes during peak hours. Perhaps most importantly, the roundabouts are safer. Before the bypass work, the signalised intersections that were replaced by roundabouts had an accident rate significantly higher than similar intersections statewide.

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 non-residential tax base.