New York State is in the process of converting State Route 17 to I-86. Almost
half of the 381-mile length of Route 17 has been designated as I-86, and several
remaining sections are either under construction or in the design phase. For the
section surrounding Exit 131, NYSDOT Region 8 required a highly detailed digital
terrain model (DTM) survey and called on Erdman Anthony for an approach that
would leverage the latest technology.
Erdman Anthony recommended
combining terrestrial LiDAR to survey the road and highway surfaces with
conventional topographic surveying to create a highly detailed and accurate DTM.
LiDAR is an acronym for light detection and ranging, also commonly referred to
as laser scanning. Terrestrial LiDAR quickly and accurately collects spatial
data from a safe location, a feature that made it the perfect field data
collection tool for busy highways like Route 17.
Laser scanning emits
laser pulses in a predefined array pattern. When a pulse reaches a solid object,
it reflects off the object and back to the scanner. XYZ coordinate values are
calculated for the point on the object. That coordinate point is assigned an
intensity value, based on the strength of the return signal. By recognizing
changes in intensity value between points, different materials, such as asphalt,
concrete, stone, and paint stripes, can be identified. When all of the points
are assembled, they are known as a "point cloud"—and form a 3-D representation
of the highway surface with photograph-like quality.
traffic lane closures would be necessary on busy highways like Route 17 while
surveyors complete their work. Yet lane closures are costly, requiring an
additional crew of highway workers to man flags or set up traffic cones or other
traffic-control devices. By eliminating the need for workers to actually enter
the travel lane, laser scanning avoids costly and disruptive lane
Following the scan and creation of a point cloud, Erdman
Anthony's survey technicians digitized cross-sections at 2-meter intervals along
the highway pavement surface. The points were given codes to identify the
feature being digitized and then joined to create a DTM of the highway surface.
Since cross-sections by traditional surveying methods are typically measured
every 15 meters, the resulting DTM was far more detailed.
result? The difference between the existing surface and the proposed 3-D model
will exceed the latest tolerances in construction technology. In the world of
GPS-guided construction machines, contractors can notice even the slightest
variation in design cuts and fills. Even an inch or two of variance in materials
like asphalt compounds greatly over a multi-mile stretch of highway and can lead
to significant cost overruns. By designing off an existing surface modeled from
scan data, Region 8 can be assured of highly accurate material bid quantities.
Through laser scanning, Erdman Anthony met NYSDOT's needs by providing a
DTM in a safe, highly detailed, and cost-effective manner. Upgrading the highway
to Federal interstate standards is expected to create tremendous opportunity for
economic development in New York's Southern Tier and Lower Hudson
This project is the largest terrestrial LiDAR survey completed to
date on a NYSDOT project. Erdman Anthony intends to study various technical
aspects of the project to reveal recommendations for future best practices.
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