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"It's extremely hard to hold that tight of tolerance accuracy on a paving project," notes Paul Sowa, project engineer. "Most contractors won't warranty a project that's under two percent. And on this project we had some areas (around the drainage grates) where we had to maintain a .58 and .63 percent slope. But by using the GPS with the laser augmentation system on the grader and the Trimble Control System during paving, we were able to deliver those tight specifications."

Sowa explained how he used the Trimble Business Center software to develop cross-sections of the project, which he then provided slope information to paver operators who were able to enter that information into the slope control units on the paver.

"When you're dealing with such minimal slope specifications, it would be practically impossible to achieve without the technology. You would always have the potential for birdbaths (small puddles) if you tried to constantly manually adjust the slope while still trying to pave a surface that's nearly level," Sowa explains.

Using a Roadtec RP 185-10R paver equipped with the Trimble PCS400 Paving Control System, Yates paving crew had no trouble in maintaining the required one percent grade slope right to the installed drain system. The paver was equipped with dual averaging skis and six Trimble ST200 sonic tracers (three on each side) to match asphalt slope requirements to the drain grates, and the averaging system input from the non-contact sensors allowed the crew to gradually work out the roughness that existed around the drain openings.

The system also allowed the paving crew to hold the grade while traveling over the drain grates. Other systems Yates used on the project did not provide that capability because the sensors would take readings off the steel grates and off the openings in the grates, constantly moving up and down adjusting the depth the sensors were picking up.