North Carolina regional rail project drives GPS down a different track, delivering speedy and accurate results.



Using the existing aerial data as a foundation, Strout and his team set out to build the centimeter-grade control network that would become the heart of all subsequent survey activities.
Just about anybody can run a GPS receiver; understanding the quality of the data that is collected, and the procedures required to analyze and adjust that data on large, close-tolerance projects takes a little more knowledge,” says Gordon Strout, senior project manager with ARCADIS G&M of North Carolina Inc. (ARCADIS), a surveying firm based in Raleigh, N.C. “This project has enabled us to reach a whole new level of GPS application.”

The project he’s referring to is the $724 million, 35-mile Phase I Regional Rail System, an innovative commuter rail conceived by the Triangle Transit Authority (TTA), a regional public transportation organization that serves North Carolina’s Durham, Orange and Wake Counties. Built primarily within the right of way of an existing freight railroad system, this new rail is expected to transport more than 28,000 riders daily within the Raleigh-Durham/Chapel Hill Triangle Region by 2025.

Two years ago, TTA contracted ARCADIS to assist in building the detailed base mapping framework for this project—and to do it quickly to enable construction to begin by 2005. ARCADIS’ technology of choice was GPS, operated in a variety of modes including static and RTK. “I can remember first conceptualizing the project and thinking that GPS would certainly be of help,” Strout says. “I quickly realized that it could transform our whole approach. In fact, GPS has become the cornerstone of our subsequent proposal to the TTA, and we were able to show them a significant cost saving over other methods.”

ARCADIS workers established a 400 vector, centimeter-grade GPS control network in two months, then used it to survey more than 330,000 feet of track.

A Network of Large Proportions

TTA’s Regional Rail System includes a 35-mile double-track system built along the existing North Carolina Railroad and CSX Railroad freight lines. When complete, bi-directional diesel rail cars will run on these tracks and link Durham, Research Triangle Park, Morrisville, Cary, downtown Raleigh and North Raleigh, with a total of 16 stations.

Although conceptually in the works since the mid-1980s, most of the preliminary planning and design work has been completed in the past few years. This enormous project will require not only many miles of new track, but the widening of railroad beds, the redesign of about 35 bridges, addition of a number of new overpasses and the relocation of numerous utilities. What’s more, the entire railway will be underground through downtown Raleigh.

TTA planners used aerial photography shot along the existing railroad corridor in 1997-1998 as a basis for preliminary design. The photography was accurate to within a couple of feet and referenced to a local coordinate system. Moving toward final design in early 2001, TTA looked to ARCADIS to supplement the aerial photography with higher accuracy data in preparation for detailed design—and to do it in a preferred time frame of less than three months. Using the existing aerial data as a foundation, Strout and his team set out to build the centimeter-grade control network that would become the heart of all subsequent survey activities.

With help from industry experts Earl Dudley Associates of Charlotte, N.C., and Leica Geosystems of Atlanta, Ga., ARCADIS established a 400 vector, centimeter-grade GPS control network in just two months—and then used it to survey more than 330,000 feet of track. Strout called on a crew from Earl Dudley and on Leica technical support to help select the right survey methodology to begin the project and to ensure quality control throughout the entire survey.

Simultaneously, Strout and his team began coordinating the extraordinarily complex logistics of working on a live railroad. Organizing a required safety training course for 40 staff members and subcontractors was just the beginning. Arranging for railroad flaggers, learning the train schedules and time windows, and establishing the reporting protocols to railroad trackmasters, trainmasters and other officials took a strong focus. Strout recalls a number of sleepless nights during the planning of this effort. “Beyond the technical complexity of the project, safety was our No. 1 priority and concern,” Strout says. “All the achievements of a well-run project mean nothing if people become injured.”

In early March of 2001, armed with a comprehensive plan for a high-order, high-accuracy network and being well-educated on safety issues, ARCADIS workers began recovering existing high-order geodetic monuments located along the corridor. These served as the basis for establishing about 60 primary control points along the railroad corridor. ARCADIS workers then called together personnel experienced in the use of GPS from three regional offices, collected 12 of Leica’s GPS System 500 and System 300 receivers and got to work. Working six days a week—from 7 a.m. to dusk—the survey team used static GPS to build the network step by step. “We were surveying up to three miles a day, running all 12 GPS receivers,” Strout recalls. “Our survey teams occupied control points for upwards of two hours with multiple occupations and a lot of redundant vectors. In fact, there were a total of more than 400 vectors. It was a fantastic opportunity to build a network of this caliber and size.”

He adds that the most surprising aspect of these surveys was the amazing signal reception, particularly along a corridor such as this. “People often think a rail corridor is wide and open. Not so in North Carolina,” he explains. “This corridor was established in part as far back as the late 1800s, and the surrounding landscape includes heavy canopy, significant overgrowth and infrastructure.”

However, backed by the latest GPS signal reception technology, the ARCADIS team found only one 700-foot section of track with extremely heavy canopy where the GPS couldn’t receive a signal. “Leica’s receiver technology made a quantum leap with the 500 series equipment,” Strout says. “As the lead surveyors on this effort, it rested on us to get the job done quickly and accurately. We had a lot of designers who were eager for this data.”

The subsequent network was complete in late April—one month ahead of schedule—and serves as the current control for the entire project team, designers, contractors and the client.

ARCADIS workers recovered old points and retraced surveys to recreate a continuous right of way line that had never been surveyed in its entirety before.

A Network Designed for Multiple Tasks

For ARCADIS, this extensive and highly accurate GPS control network was far more than just the foundation for accurate base mapping; it was designed to provide a framework for all subsequent survey, design and construction activities. Strout recalled the long hours spent planning the location and density of this network emphasizing, “We really wanted to maximize the benefits of this network for all activities, from right of way property surveys to as-built and utility surveys. We anticipated the range limitations on real-time GPS activities and built the network density accordingly.” It’s a plan that paid off during recent property surveys along the northern portion of the corridor, another huge phase of this multifaceted project.

From downtown Raleigh, north for about 10 miles, there are some 200 tax parcels on the east side of the rail corridor alone, as well as thousands of maps, deeds and other documents that date back more than 100 years. It was up to ARCADIS workers to recover old points and retrace surveys to establish the complex history of this corridor, recreating a continuous right of way line that had never been surveyed in its entirety before. Working closely with TTA’s attorneys over a period of about 12 months, and painstakingly pouring through rooms of maps, deeds, old encroachment agreements and other historic documents, ARCADIS surveyors meticulously pieced together an amazing puzzle.

A common misconception is that a railroad line is built along open areas that are easily walked and crossed. Nothing could be further from the truth in this case. Fences, buildings and other improvements have accumulated along the railroad right of way for a long time. Thick hedgerows of thorny bushes, poison ivy and debris create some of the worst visibility in the area. Using RTK GPS and the high-accuracy GPS control network, the ARCADIS survey team was able to get in and out of these tight and somewhat dangerous (for those wary of unfriendly wildlife and poisonous plants) places with no disturbance. In the end, Strout and his team were able to meet TTA’s requirements for positioning, accurately locating everything from dog pens to air conditioning units. Strout’s team took approximately five months to complete this field effort. “GPS allowed us to finish this job within a very short window of opportunity—often just a couple of hours a day depending on railroad right of entry agreements, flagger contracts and train schedules,” Strout says.

Strout’s control network remains intact after more than two years, providing the single source of horizontal and vertical control to date. As crews move into position to begin construction, and as final design begins in earnest, ARCADIS workers seek to increase the network density from 60 points to 150 points to provide even better one-stop centimeter accuracy control for these upcoming activities. A job this big employs multiple surveyors and engineers throughout its design and construction life span. With a permanent control network, all of these agents can use the same network, greatly minimizing the chance for error.

As ARCADIS manages this job, Strout reflects back on the benefits of good planning. “GPS is such a tremendous tool in our business, helping improve speed, accuracy and mobility," he says. "However, used properly and to its fullest capability, it can also facilitate numerous activities beyond the original application. Better yet, it allowed us to meet—and beat—our client’s tight time schedule, thereby allowing designers and contractors to stay on schedule with upcoming construction and design timelines." Smiling, he adds, "I’m sleeping just fine now."