Road surface markings convey traffic information and provide guidance to drivers and pedestrians. In the United States, standardized markings usually separate traffic lanes, indicate stops, regulate vehicle flow, and mark parking spaces.
Surface markings worked well for decades with Departments of Transportation constantly searching for better methods to improve marking visibility and placement. As with any road material, markings must be maintained and updated periodically to offer the safety advantages to motorists.
For most roads, the DOT painted or taped stripes to road surfaces. Better visibility paints and tapes have increased safety for night driving and retained their reflective properties longer. As traffic increases and road maintenance equipment brush or scrape the road surface, paints and tapes lose some of their materials and their reflective properties.
For approximately 20 years, a new method has been tried and used to install pavement markings that last longer than one to two years. When the road is in the paving process, mostly with concrete roads, grinders dig a depression where pavement markings are designated. Contractors use equipment to paint or hand-place the tapes after the pavement cures and the markings are even with the road surface. This process debuted in the Upper Midwest in the mid-1990s.
Road marking deterioration
In South Dakota, the DOT began trying recessed pavement marking in 1995. Jason Humphrey, construction and maintenance engineer, said, “What we were encountering was that our pavement markings were deteriorating too quickly. We attributed the deterioration to traffic wear and snowplows scraping off the pavement markings.”
The DOT learned about a new method of applying pavement markings through counterparts in other states and other organizations that experimented with recessed pavement markings. “We started trying this method on a limited basis, particularly on the more expensive pavement markings of the three grades,” said Humphrey.
“One is tape applied to roads. We use that mostly in towns and municipalities. Second, we have a more durable type of pavement marking, an epoxy type of paint that is intended to last longer under high traffic areas. We can expect five or more years out of this paint if we can protect it. Then we have what we call our normal grade of paint, a water-borne paint that we expect one to two years of life,” Humphrey explained.
On South Dakota roads, the DOT will grind grooves approximately five inches wide and place four-inch wide tape in the groove. “We use this method predominantly in concrete pavements, the tape is hand-applied in the groove while paint is applied in other areas of the road.
Method used increases
“We’ve seen an increase in pavement markings ranging from two to five years in extra life across the state. This method provides a significant savings for us, and we’re increasingly using more of this application,” said Humphrey noting that South Dakota interstates and state highways using portland cement concrete have turned to recessed pavement markings.
McLeod County, in central Minnesota, was the first to use recessed pavement markings in the state in 2009. County highway engineer John Brunkhorst said Hoffman Construction, Mankato, suggested the county try this method. “We received this suggestion from Ken Hoffman and tried this method first on County State Aid Highway (CSAH) 7 for 2.5 miles.
“It was an asphalt road. We milled it and put a five-inch concrete overlay on top. When the concrete was still fresh, the contractor made a depression using metal plates attached to the back of the texture cart.
“The metal plates were four inches wide to make grooves in the concrete and was the last operation before applying the curing compound. The concrete required seven to 10 days to cure, typically, to get strength. The subcontractor sandblasted the curing compound from the grooves, then applied epoxy into the grooves,” Brunkhorst said.
Standard epoxy paint
The epoxy paint is a standard Mn/DOT specification that takes about four minutes to dry in the grooves but does not stick to the curing compound. That’s why the curing compound must be sandblasted from the grooves. “Typically, every concrete paving job requires sandblasting the curing compound from the concrete before applying pavement markings. We anticipate repainting the markings every so many years depending upon how they wear,” said Brunkhorst.
After two years, CSAH 7 performs very well, according to Brunkhorst. “The biggest benefit we see is we don’t have the snowplow damages on the paint. We don’t foresee repainting the pavement markings for four to five years. On the first job, the contractor bid 30 cents a foot to install grooves but for the last two projects, the contractor bid only one cent a foot so this process paid for itself in a short time.”
After McLeod County initiated this process in Minnesota, Clay County engineers saw the publicity and decided to use recessed pavement markings. “We call it a grooved-in stripe,” said assistant county engineer Nathan Gannon. The northwest Minnesota county used this method on a re-grade of CSAH 11 and on the CSAH 52 unbonded overlay. “Originally CSAH 52 was a concrete road with an asphalt overlay installed in 1978. We milled the asphalt, put down a bond breaker, and put on a six-inch concrete overlay.
Ski depressed groove
“The contractor used a weighted ski that the equipment picked up and dropped to depress the groove. On the edge lines, we used a seven-inch wide ski to make the groove and on the center line, we used a five-inch stripe. We sandblasted the texture and, after the pavement cured, we sandblasted the curing compound and placed the epoxy,” said Gannon. A striping truck travels along the road to place epoxy in the grooves, and after a few minutes, the epoxy dries.
“Both highways received new pavement markings in 2010, and they’re performing very well to benefit the user. The stripes are not destroyed like it normally does after snowplowing,” said Gannon. “We’re two years into this new method, and we’ll see how long the paint lasts. We are anticipating this new method will extend the life of the paint on the highways.”
Gannon said Clay County has about 350 miles of paved roads. “On our concrete roads, we’ll increasingly use this method.”
Most paving contractors devise a method to make grooves for pavement markings. PCi Roads, Rogers, Minn., welded metal plates in the needed sizes to the paver’s pan. “While we were paving, we formed the grooves in the edge lines and the center line,” said Steve Gerster, vice president.
On Anoka County Road 22, PCi Roads worked on the concrete overlay and made grooves in the road while the paver slipformed the concrete. The specifications indicated a groove at 1/8 inch, then workers waited for the road to cure and paved the road shoulders during this time. “The stripes are the last to be put on the road surface, and the road must cure for about five days before vehicles can travel on it,” said Gerster.
Recessed pavement markings continue to outlast traditional pavement markings and save money in states where snowplows destroy some of the markings every time they scrape the roads. For most county and city governments, that means more money in their road maintenance budgets. n