The Tesla runs on a Windows Mobile 6.5.3 operating system and has WiFi and Bluetooth wireless technology. The ultra-bright, backlit LCD screen measures almost 6 inches and the unit weighs less than 2 pounds and is 5.3 inches wide and 8.6 inches long.
The software allowed Banks to check cuts and fills, layout points and the survey at various areas of the jobsite and gave one person control over grading for multiple machines. Cox said the Tesla’s capability of rapidly tracking multiple signal transmitters was a big plus and the software’s ability to handle large surface files and linework files gave Banks powerful data access on location.
Dual Millimeter GPS+ antennas were set up on a Wirtgen 2200 SM (Surface Miner) so that the milling depth could be monitored on both sides of its 12½-foot-wide passes.
The milling subcontractor, PP&S Inc., Greenville, SC, also used a Wirtgen W 200 cold milling machine that milled the shoulders with 6½-foot-wide passes. Two Roadtec 195 pavers equipped with Eagle screeds also had dual Millimeter GPS+ capability.
Near the north end of the project, a HiPer+ base station was set up in the highway median. Because this covered a long distance as most paving projects do, an external 35-watt radio was added to the HiPer+ base station to ensure the reliability of the latter’s signal transmission.
By comparison, the HiPer+ base station’s built-in radio has 1 watt of power, which is adequate in most situations.
“We had some minor issues occasionally due to being at the bottom of the hill, for example,” Cox said. “But we were still getting signals. In those situations, there was just a two- or three-second lag between base shots.”
Off to the side on the outside shoulder, four PZL-1s were set up and spaced at roughly 800 feet, providing a total of more than half a mile of laser coverage. As needed, the transmitter located farthest from a milling machine or paver would be moved to the front of the line.
“The milling machines traveled maybe 30 feet a minute and we never stopped once to wait on transmitters to be moved ahead,” Cox said.
The milling machines milled to full depth on one pass. The outside lanes were 12 feet wide with a 10-foot shoulder and the inside lanes were 12 feet wide with a 4½-foot shoulder. Then the milling machines made a second pass to mill the shoulders; the Wirtgen 2200 milled the lanes and the Wirtgen 200 milled the shoulders.
Randall Brown, owner of Georgia Surveyors Exchange, pointed out that the grading system is particularly beneficial when variable-depth milling and paving are necessary because it essentially turns a two-step process into a one-step process.
“The biggest thing on this project above and beyond the cross-slopes was the variable depth,” he said, noting that a CAD file incorporating the variable pavement depths was used as the basis of 3-D file loaded into the system. Automated grade control eliminated the need for marking the variable depths on the pavement.
“Traditionally, with a milling machine, you’d be setting up a measurement for elevation and cross-slope and use a sonic tracker. The sonic tracker will handle the elevations and a slope sensor will handle cross-slope, but you’d have to rely on the operator to manually handle the variable elevation and cross-slope changes by reading marks on the ground and operating the machine freehand.”
The first lifts of new asphalt were staggered and then the Millimeter GPS+ was used for joint-matching, with positive results, Cox added, much to his delight. He reported that shots of the pavement during milling had an average accuracy of two-hundredths of a foot.
Cox noted that automated grade control made a big difference on this challenging project. For example, every bridge approach along the route was milled and paved using the Millimeter GPS+ system and the cross-slope was checked for an accurate tie-in with the new pavement using an inclinometer, and the automated grade control was consistently accurate. Most importantly, the use of the system translated to real dollar savings for taxpayers on this project. According to Cox, the use of automated grade control saved $20,000 in direct costs and $50,000 in labor costs because milling and paving lifts were done right the first time within such a tight timeframe.