Georgia Tech researchers have developed a safer automated system for installing the ‘cats-eyes’ type small, reflective markers that make road lanes more visible.
These safety devices, called raised pavement markers (RPMs), 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 centimetres from road 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) funded the Georgia Tech Research Institute (GTRI) to develop a system capable of automatically placing RPMs along the lane stripes while in motion. After three years of research and development, GTRI expects to deliver a prototype system early this year.
The engineers designed an RPM-placement mechanism using pressure-sensitive adhesive and a lane-stripe tracking system. They then developed a full-scale, lorry-mounted RPM placement system which combines the lane-stripe tracking system, electrical power, compressed air, hydraulic power, and adhesive melting and dispensing systems.
The project resulted in a prototype system capable of dispensing an RPM onto the tarmac along with the necessary hot-melt adhesive applied at 190oC while travelling at 8km/h. A pattern-change mechanism can position two placement mechanisms to accommodate any of GDOT’s five specified RPM placement patterns.
Operation of the system only requires two people. An operator on the back of the lorry 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 lorry must maintain alignment between the stripe pattern on the road and a caster wheel on a boom in front of the lorry. 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 90cm range of travel and is moved laterally to keep the placement mechanism centred along the road stripe. RPMs are then typically applied about 24m apart. It takes about 35 milliseconds from the time the edge of the RPM hits the ground to the time it is flush with the road.