DEI’s proprietary software helps the firm analyze high and low areas along the I-15 CORE alignment. Red areas indicate where the original aerial map is too high; blue areas show where the original map is too low. 

With a total projected program budget of approximately $5 billion, the Interstate 15 Corridor Expansion project (I-15 CORE) south of Salt Lake City is the largest dollar-value project ever undertaken by the Utah Department of Transportation (UDOT). The expansion is part of an 840-mile route connecting San Diego, Calif., to Salt Lake City that was identified as one of six “Corridors of the Future” by the U.S. DOT in 2007. Construction is scheduled to begin in the spring of 2010 and will involve rebuilding and expanding the capacity of I-15 to replace aging infrastructure and to meet the increasing traffic demand from Utah County, which is one of the fastest-growing counties in the nation. In 2010, the county’s population is projected to be 560,000 residents; by 2030, that number is expected to exceed 907,000.

I-15 is already a “superhighway” carrying up to five lanes of traffic both northbound and southbound. High-occupancy-vehicle lanes are planned for much of the I-15 CORE project’s 43-mile length. Along the northern portion of the project, UDOT will completely remove and replace the existing pavement and add two northbound and southbound lanes. On the south end, UDOT will add one southbound and one northbound lane. The I-15 CORE project also calls for rebuilding or modifying 11 freeway interchanges and replacing 55 aging bridges.

Performing the survey work for the project is DEI Professional Services LLC, a 26-year civil engineering and land surveying firm headquartered in Phoenix. For Phase 1, the firm was assigned to gather field measurements along a 20-mile stretch of I-15 with GPS technology and robotic total stations. Project deliverables included accurate contour maps and digital terrain models (DTMs). Since design work on the new freeway could not begin until these deliverables were available, the schedule permitted just eight weeks to complete the surveying, mapping and modeling work.

According to Jason Kack, RLS, DEI’s principal and survey division leader, the survey presented three primary challenges: the size and time constraints of the job, the need to do much of the survey work at night, and the weather. “They say it snows like crazy about three or four weeks from now,” Kack said in early October 2008. “So our last couple of weeks here should be a real adventure.”

A Labor-Intensive Project

DEI began work in late September by checking 15 existing control points using Topcon GR-3 GPS equipment in static mode and then checking 10 more points using the same equipment in RTK mode. “We established 53 new points on the primary corridor and 110 new points on the supplemental areas such as interchanges and ramps,” Kack says. “And we completed 18 miles of optical bench loops using Topcon optical levels.”

Because the existing pavement on the northern 12.5 miles being surveyed for the project will be completely removed and replaced, field measurements in that section did not need to be as accurate as in the southern section, where the existing roadway will be widened. To obtain the northern-section measurements, DEI used three field crews equipped with Topcon GPS systems, which are accurate to plus or minus 0.10 foot. “We took elevations at 200-foot intervals on the pavement and at 100-foot intervals or less on the ground, depending on what the terrain dictated,” Kack says.

On the southern seven-and-a-half mile portion of freeway surveyed in Phase 1, designers and contractors must match the edge of the existing pavement with the new structure. To achieve the higher accuracies required for this part of the project, DEI used four crews equipped with Topcon robotic total stations (two 802a units and two of the new 9000-series units). The crews set control points at 500-foot intervals along the edge of the pavement and placed two robotic total stations on each side. Each robot was set at 1,000-foot intervals and could shoot 500 feet to either side. That way, the robots leapfrogged each other as they moved down the pavement. “The robotic elevations are accurate to within plus or minus 0.02 foot,” Kack says. “But we did something different in the field for the southern section. Everywhere we took a pavement shot with a robot, we indicated flag elevations to the nearest hundredth of a foot at 50-foot intervals. The designers need our precise elevations to extend the cross-slope of the freeway.” An additional crew with GPS gathered measurements from the soft surfaces in the dirt.

“To survey 20 miles of freeway in eight weeks was quite an undertaking,” Kack says. “We needed almost twice the people to shoot the seven-and-a-half-mile section with robotic total stations as we did in the northern section.” Crews worked around the clock to gather the required measurements. DEI closed traffic lanes with reflective barrels at night and had safety crew members with flashing lights accompany the surveyors in the field to help ensure worker safety.

For night surveying, the robotic total stations were key. “We couldn’t have done that work without robots,” Kack says. “They don’t need to see like a human. They use a laser to track the rod, so they don’t know the difference between day and night.”

UDOT will add one southbound and one northbound lane over seven-and-a-half miles on the south end of the I-15 CORE project.

Putting I-15 “On the Map”

In the office, DEI used its mapping capabilities to enhance the value of its survey data. At the start of the project, the firm was provided with an existing 2-foot contour aerial map and DTM. “We collected ground elevations and then dropped them onto the existing 2-foot DTM,” Kack says. “Then we used our proprietary software to go through the DTM and analyze the variations between the existing DTM and the actual field elevations.”

In fact, DEI’s software created a color-coded map that indicates the severity of those variations. “The colors move through the spectrum,” Kack says. “The red color shows where the DTM is too high, and on the other extreme, the blue color shows where the DTM is lowest. That gave us the ability to show UDOT how far off from the desired 1-foot accuracy the existing map was.

A DEI surveyor backsights a control point to set up his robotic total station.      

“Using that ground data, we remediated the DTM to a 1-foot level accuracy, and we produced a new 1-foot contour interval DTM,” Kack says. “The design engineers can use the new contour map and DTM for earthwork analysis, grading design, and drainage studies.”  

DEI’s extensive survey resources and experience combined with its proprietary software are the primary reasons the firm was hired by Horrocks Engineering, one of the I-15 CORE project’s design firms. “Earlier mapping was done for environmental studies,” says Greg Olson, a Horrocks principal. “Rather than taking the time to re-fly the highway and map it that way, this gives us a quick way to supplement the original mapping with additional data and tighten up the original maps. The new digital terrain maps will be used to develop cross sections, earthmoving quantities and the like. The designers use it to set profiles and grades.”

The new maps also lower the risk that UDOT will face problems over earthwork quantities as earth-moving work goes forward. “When we were approached about doing additional work to improve the accuracy of the original survey, we figured that better data can mitigate the risk [of errant earthwork quantities] for both UDOT and our design-build contractor,” says Dal Hawks, PE, MBA, project director for UDOT.

A DEI surveyor working at night holds a Topcon GPS rover to collect a shot for the I-15 CORE project. 

A Supplemental Endeavor

In early October, DEI won a bid to survey 37 supplemental areas such as interchanges, ramps, underpasses and rivers. “In those areas we were shooting complete detail at 50-foot intervals,” Kack says. “We shot curbing, surface utilities, drainage structures, roadway signs, traffic signals-total detail.” For that work, DEI used Topcon robotic total stations for the hard points and Topcon RTK GR-3 units for the soft points such as natural ground and drainage ditches.

“The hard points had to be within plus or minus two-hundredths of a foot,” Kack says. “And the soft points only had to be within plus or minus one-tenth of a foot.” For the supplemental areas, the deliverables were detailed drawings in Bentley MicroStation, which is the standard design software used by UDOT. Five crews worked the supplemental areas bringing the total number of crews on the project to 13.

Despite two snowstorms, DEI surveyors completed field work on the eight-week project four days early-and surveyed two additional miles of I-15. “We had to pull off a couple of times for snow, but then we worked three Sundays to catch back up,” Kack says.

According to Kack, several factors contributed to the success of the project. “Our staff made an unbelievable sacrifice,” he says. “They basically dropped everything within five days’ notice and moved to Utah. About 75 percent of our entire field staff moved to Utah for that eight-week span.” Kack notes that Horrocks’ management of the contract with UDOT and the support of the equipment dealers that supplied the Topcon instruments were also key. “We couldn’t have [accomplished the project in the required time frame] without any one of these three factors,” Kack says.

Editor's note: In late November, UDOT put the I-15 CORE project on hold due to budget concerns. Financing discussions are expected to continue through the end of the current legislative session in March.