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Traditionally, environmental specialists and engineers have completed the EIS prior to involving surveying accurate enough for design, right of way (ROW) and construction work. In its place, they've relied on high-flight aerial photogrammetry to provide the information needed for environmental mapping concerns. Surveyors would later need to tie their higher accuracy control and the lower accuracy EIS data together into a common coordinate system. With the advent of precision surveying and specifically the Global Positioning System (GPS), new processes are being developed in some states that incorporate this high level of surveying from the start of the study.
"Before GPS, surveying needs were a bit of an afterthought to environmental concerns," said Dan Smith, PLS, statewide survey coordinator for the Colorado Department of Transportation (CDOT). "But GPS has enabled states to build High Accuracy Reference Networks (HARNs) that can provide high-accuracy coordinates throughout the project. CDOT is increasingly including surveyors in the EIS: it's a new way of thinking that is making transportation project surveying seamless and changing the way we do environmental planning."
CDOT believes this approach benefits all involved, providing highly accurate data for every aspect of the EIS. In addition, using precision surveying from the start provides a common control network for the entire project, increasing efficiency, accuracy and productivity. CDOT's current U.S. 36 project shows this "new way of thinking" in action.
U.S. 36One of the main corridors in the Denver area, U.S. Highway 36 connects Denver with Boulder, approximately 25 miles to the northwest. This corridor has experienced substantial increases in congestion and is the focus of a multi-year transportation improvement study. Today, a consortium of government agencies and consulting firms is conducting an EIS to identify multi-modal transportation solutions, including highway improvements, Bus Rapid Transit (BRT) and commuter rail transit. Lead agencies include the Federal Highway Administration (FHWA) and Federal Transit Administration (FTA) in cooperation with CDOT and the Regional Transportation District (RTD).
From the start, the project team included DOT surveyors. Rather than only completing the high-flight aerial photogrammetry traditionally used for EIS requirements, CDOT requested up front the high-accuracy low-flight aerial photogrammetry needed for the design phase. CDOT surveyors also ran a first-order level line for the corridor and tied it into their GPS control network.
"We could be using the first-order bench marks in this corridor for the next 30 years," said Jeff Wassenaar, PE, CDOT engineer and U.S. 36 project manager. "We'll base our EIS preliminary draft, design and construction on these. The work has to happen anyway; it benefits everyone to do it early."
CDOT Surveyors Joe Gunderson, PLS, and Scott Kimminau, PLS, took on the project in January 2003. The multi-year project included the first-order levels, high- and low-flight aerial photogrammetry, as well as all design, ROW mapping and construction survey work required throughout the entire project.
"In the past we wouldn't get on board until much later in the game and then we'd have to play catch-up," Kimminau said. "That's hard to do--and it holds up conceptual design and photogrammetry. If they were waiting on something from us, they'd be stuck. But now we can provide a solid groundwork and good survey support for the entire design project."
Initially, crews ran first-order levels to get vertical control, tying about 52 new bench marks into three existing National Geodetic Survey (NGS) benchlines. The new benches will be bluebooked, adding to the high-accuracy control in the corridor and benefiting area cities, counties and private surveyors.
Simultaneously, crews provided points for high-flight aerial photogrammetry to establish a coordinate base. Gunderson's crews used GPS to set, panel and occupy 48 new points and the appropriate HARN points; they later added 298 points and the first-order bench marks to densify control for the low-flight photogrammetry. Those panel points that were within the "build corridor" were set as more permanent markers. These "control monuments" will be used through the design, ROW and construction phases.
By using nine crews with GPS receivers including the Trimble RTK GPS 5700, Trimble 5800 and Trimble R-8 systems, CDOT was able to perform GPS fast static sessions of the entire high-flight control network in three and a half days. They later used the same crews and equipment to perform fast static sessions of the low-flight network in eight days.
Crews set the points, paneled them and had them flown. High-flight elevation control was based on the HARN and existing first-order benches; low-flight was further vertically constrained using the new bench level run. Crews used the 'leapfrog' method to migrate through the network, minimizing the influence of centering error over the points.
"GPS expedites all the processes involved in setting photogrammetric control," said Gunderson, survey lead. "Because of the corridor's size you'd have double or triple the number of points--and the time involved--if you used optical systems."
"They had no idea that we were so far ahead at this time," Kimminau said. "Their schedule had been accelerated; they said if we hadn't had the high flight on board already they would've had little chance of meeting that schedule."
The low-flight control network also enabled the survey crews to provide some immediate design support, gathering real-time kinematic (RTK) GPS info on 35 structures such as bridges, decks, and sound and retaining walls.
"The low-flight data was "final adjusted" with our software [Trimble Geomatics Office], establishing an excellent control network," Gunderson said. "Having both GPS-derived elevation and first-order bench marks tightened up the vertical remarkably. I don't think anything varied by more than plus or minus four hundredths of a foot."
Another task accelerated by incorporating precision surveying early in the EIS is establishing the ROW corridor. By taking Geographic Information System (GIS) data from several cities and counties in the project area, the crews created a rough AutoCAD (Autodesk) drawing of the corridor. They then tightened the accuracy by adjusting it through section corner data they had gained through fast static GPS sessions. From this they'll determine ROW needs and property descriptions.
"Without the section corners, all we'd be able to provide is a pretty picture that doesn't necessarily fit what the right of way and property lines are out there," Gunderson said. "To be able to calculate the impact on property with confidence we need precise control. And we already have that in place."
Once the final design is determined, they'll be able to finish the ROW process quickly, enabling timely acquisitions and speeding up the entire project.
Precision surveying also positively impacts the EIS, according to Wassenaar. By providing high accuracy data to environmental specialists mapping such areas as wetlands, wooded areas, endangered wildlife concerns and cultural resources, they'll have precise data for their mapping and decision-making needs.
"Doing precision surveying within the scope of the EIS makes a lot of sense for a lot of reasons," Wassenaar said. "It makes connectivity reliable and precise, enables good planning and accurate details from the start and provides more reliable data to your stakeholders, the public and governmental agencies. Without a good base, it's hard to do precise mapping later in the project. With a common coordinate base, all parties involved can communicate more effectively from the very beginning."
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