A bunch of professors armed with a gadget called a "retroreflect-o-meter" say painted roadway markings like the stripes dividing lanes are much more effective if they're applied in the same direction the traffic flows.
That may seem like a classic "so what" kind of discovery, but the researchers behind the North Carolina State University study (.pdf) say the findings could help state and federal highway authorities comply with forthcoming federal safety regulations and save millions of dollars on paint.
Some 60 percent of the nation's roads are marked with paint, and study co-author Dr. Joseph Hummer says the "retroreflectivity values" of such markings are higher in the direction of the striping. In other words, the paint reflects more light if the paint truck is going the same direction as traffic. The difference is equivalent to about a year of wear and tear, meaning the markings will look "one year newer" if you're going the same direction the paint truck was.
Hummer says the discovery could help federal and state transportation departments more accurately predict the frequency with which roads must be painted - an endeavor that can cost $2,000 to $3,000 per mile - and better develop a standard for measuring the brightness of painted traffic markings.
More importantly, Hummer told us, it could increase safety.
A couple grand per mile may seem like a lot of money for paint, but it's still cheaper than using thermoplastics and other materials.
Paint takes a beating under all those tires, though. Roads in the northeast take the most abuse during the winter. Snow tires, road salt and snowplow blades play hell on the paint, which is why Massachusetts has to repaint its roads every two to three years and Maine slaps a new coat on 8,000 miles of road every year, according to The Boston Globe.
When roadways are restriped, glass beads are scattered onto the paint (see the photo) to make the markings reflective. The researchers found those beads tend to bounce and roll because the paint truck is moving, reducing reflectivity. "The beads skid and build up paint on one side," Hummer said. "Therefore, they are less reflective in that direction."
The Federal Highway Administration is drafting new standards dictating how and when road markings should be applied. Hummer says his findings raise the possibility a painted line could pass the new brightness standard if tested in one direction but fail if tested in the other.
Hummer realizes most paint trucks travel in the same direction of traffic but says his study is more concerned with the lines dividing opposing lanes of traffic - like the yellow dividing lines in the main photo - because those tend to be painted simultaneously. That makes them brighter in one direction than the other. "The center line is the most important line on the road, and it's brightness will have an effect on the way we drive," he said.
Don Rowell, a regional sales manager at Advanced Traffic Markings, said he couldn't comment on Hummer's findings until he'd read the study but says one must also consider the cost-effectiveness of shutting down both lanes of traffic to restripe a road. His firm carries a wide variety of road marking equipment but doesn't offer paint. Instead it sells plastic tape. It costs 40 cents more per foot than paint, but it already has the glass beads embedded in it, rendering the reflectivity issue moot.
The study, "The Impact of Directionality on Paint Pavement Marking Retroreflectivity," appears in the journal Public Works Management and Policy.
Photos: North Carolina State University
