Automated System Installs Pavement Markers

There are more than three million of these safety devices, called raised pavement markers (RPMs), in service on Georgia highways. They are installed and then need to be replaced about every two years by road crews who consider the task one of the riskiest they face. Workers typically ride on a seat cantilevered off the side of a trailer just inches from highway traffic.

Manual RPM placement is not only risky for personnel, but it is also expensive and time-consuming. A typical RPM placement operation includes four vehicles and a six-person crew. All the vehicles must stop at each marker location, so there is tremendous wear on the equipment and increased fuel use.

The Georgia Department of Transportation (GDOT) believed there was a better way to do it and funded the Georgia Tech Research Institute (GTRI) to develop a first-of-its-kind system capable of automatically placing RPMs along the lane stripes while in motion. After almost three years of research and development, GTRI expects to deliver a prototype system early this year. Because of widespread interest in the system, researchers will present a report on their project on Jan. 23 at the National Research Council's Transportation Research Board Annual Meeting in Washington, D.C.

"The advantages of our automated system are: it's less labor-intensive, it's faster and safer, uses less fuel, and it causes less wear and tear on GDOT equipment," explained project manager Wiley Holcombe, a GTRI senior research engineer.

Engineers conducted the work in two phases. First, they designed an RPM-placement mechanism using pressure-sensitive adhesive and a lane-stripe tracking system. Then, they developed a full-scale, truck-mounted RPM placement system. It is based on a single GDOT-owned truck and includes the lane-stripe tracking system, and electrical power, compressed air, hydraulic power, and adhesive melting and dispensing systems. Some components of the system were off-the-shelf parts, but the GTRI Machine Services shop fabricated most of the custom components for the system, Holcombe notes. After some field-testing, the project resulted in a prototype system capable of dispensing an RPM onto the pavement along with the necessary hot-melt adhesive applied at 380 degrees Fahrenheit while traveling at 5 miles an hour. A pattern-change mechanism can position two placement mechanisms to accommodate any of GDOT's five specified RPM placement patterns, Holcombe explains.

Operation of the system only requires two people. An operator on the back of the truck loads the adhesive melters with adhesive and stacks RPMs in the hoppers from which they are dispensed, depending on the placement pattern. Meanwhile, the driver of the truck must maintain alignment between the stripe pattern on the road and a caster wheel on a boom in front of the truck. Also, the driver touches a computer screen in the cab to indicate to the placement system the new stripe pattern each time the caster wheel crosses a stripe pattern change.

RPMs are dispensed from the hoppers onto a loader arm, which deposits them onto a telescoping slide that connects to a placement mechanism on an attached carriage. The carriage has a 3-foot range of travel and is moved laterally to keep the placement mechanism centered along the road stripe. RPMs are then typically applied about 80 feet apart. It takes about 35 milliseconds from the time the edge of the RPM hits the ground to the time it's flush with the road, Holcombe notes.

"The GDOT's primary use for the automated RPM placement machine will be placing markers on the skip lines for interstate and multi-lane highways," said GDOT spokeswoman Karlene Barron. "These types of routes pose the highest safety risks to our employees and equipment.

"The GDOT also plans to use the system on high-traffic-volume secondary or two-lane roads, when possible," Barron added. "Using the automated system, we will not have to stop at every placement, which will increase safety and productivity plus reduce wear and tear on GDOT equipment. Plus the operator will be high on the back of the machine instead of near ground level."

Six of GDOT's seven district offices have their own RPM placement crews, and there are four other crews that work statewide. GDOT also plans to use the system in the metro Atlanta area.

GTRI's automated raised pavement marking system could be used outside Georgia, though Holcombe explains that its design is most appropriate for Southern states with warmer climates. In regions that get a lot of snow, RPMs must be applied somewhat differently to reduce the risk of damage to RPMs by snow-clearing equipment.