A quick survey

News April 04, 2002
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Using Cyrax scanning technology, David Evans and Associates Inc

Using Cyrax scanning technology, David Evans and Associates Inc. surveyed 24 bridges in 40 days without disrupting traffic on the heavily traveled I-25 through the Denver, Colo., metropolitan area. T-REX, the Transportation Expansion Project launched by the Colorado Department of Transportation (CDOT), includes highway expansions, improvements and the addition of light rail along 18 miles of I-25 and I-225. The $1.67 billion design-build project includes reconstruction of interchanges and bridges, a new drainage system and improved pedestrian and bicycle access. One of the goals of the project is to accommodate the addition of a light-rail along sections of the interstate.

CDOT selected Southeast Corridor Constructors (SECC) for the project, based in part on SECC's aggressive work plan for finishing T-REX 22 months ahead of CDOT's schedule. SECC is a joint venture between Kiewit Construction Co. and Parsons Transportation Group (PTG). Turner Colley Braden (TCB), Sverdrup and DMJM are assisting PTG in the project design. Kiewit is responsible for gathering the necessary design survey information as well as construction staking and final right-of-way surveys. David Evans Associates was hired as the design contractor of the project.

Time was a critical element, as was the need to avoid lane closures during surveying. A total of 22 structures (out of a total of 67) needed to be surveyed with a combination of Cyrax and other terrestrial survey methods in 40 days.

The way it was handled

Crews used one scanner mounted on a tripod and the other scanner mounted on a boom truck, dubbed the "Scan Van". The tripod scanner performed the under-bridge scanning and tight area work, while the Scan Van provided proximity for the railroad scanning and mainline work. The Scan Van has a boom arm that raises the scanner up and increases the range and visibility, thus increasing the amount of data that is captured. Crews could park off the shoulder with the van and scan the freeway while the cars drove by. The cars would show up in the scan as a single line. The scanning technicians could then delete the cars from the scan before sending the data to the mapping technicians. If the traffic is going very slow or was stopped there was no attempt to scan.

Crews also learned that by setting up a conventional instrument, such as total stations with each scanner, they were able to increase productivity. They could tie in the control points while the scanner was operating and pick up the obscure area topo that the scanner could not observe. The scanner can only pick up what it can see, therefore the top of a curb may be mapped but the flow line would not be measured. Likewise, workers found that areas around parked cars, guardrails or brush could be mapped using the conventional instruments.

For more on the story, read the April issue of Roads&Bridges magazine.

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