All better

FHWA program helps improve pavement marking

Julie Zirlin; Contributing Author / May 01, 2015

When 3M wanted to test a pavement-marking system that could make it easier for drivers to find their way through work zones in dark, rainy weather, the company turned to the Federal Highway Administration’s (FHWA) Highways for LIFE Technology Partnerships Program.
 
Wet road conditions can make it hard to see conventional pavement markings, particularly in work zones, where lane shifts and other new traffic patterns are common. The 3M All-Weather Paint for work zones incorporates specially designed wet-reflective optical materials into pavement-marking paint to make driving lanes more visible and work zones safer for both travelers and construction workers.
 
The St. Paul, Minn., company used a $499,000 grant from the Technology Partnerships Program to refine the pavement-marking system and evaluate it in work zones in North Carolina and Ohio. The goal of the Technology Partnerships Program is to move technologies currently in the prototype phase closer to market. The program considers technologies that boost highway safety or quality and cut congestion. The program also promotes partnerships with state and local highway agencies to demonstrate the innovations in real-world settings.
 
Since 2007, FHWA’s Technology Partnerships Program has awarded eight competitive grants to industry to test promising prototypes in safety-, bridge- and pavement-related areas. Two additional projects are evaluating the performance of commercially available highway-safety innovations, and more grant recipients are expected to be announced in 2012. The Technology Partnerships Program is part of FHWA’s Highways for LIFE initiative to encourage rapid adoption of innovations that improve the nation’s transportation system.
 
The Technology Partnerships approach fills a critical gap in the development of innovations that can benefit the highway system. The program capitalizes on the creativity of the private sector by providing funds at a stage of innovation development where the proof of concept has been established. FHWA acts as a broker between the private sector and highway agencies that are willing to demonstrate and evaluate these promising technologies.
 
Visible when wet
The all-weather pavement-marking system consists of high-build waterborne paint and glass beads, which provide good visibility in dry conditions but can be hard to see in the rain. It also includes optical elements made of a ceramic core surrounded by tiny, high-refractive-index beads. This second set of beads provides improved retroreflectivity in wet conditions.
 
The goal of the Technology Partnerships project was to develop a market-ready pavement-marking system that maintains adequate visibility and enhances driver safety but also meets work-zone requirements such as faster application and drying times and cost efficiency.
 
The Technology Partnerships project enabled 3M to put the all-weather pavement-marking system through its paces in a two-phase evaluation process. In the first phase, the company used three prototype versions in a human-factors study at the Texas Transportation Institute. The prototypes, along with a temporary wet-reflective tape and paint with conventional glass beads, were applied to a closed course with a section where artificial rain could be generated.
 
Thirty participants evaluated the pavement-marking systems under dry, rainy and wet—just after rain—conditions while driving the course at night. Their task was to identify the earliest point at which they could see a change in delineation. All three prototypes performed equivalently under all conditions and significantly outperformed the conventional markings under wet and rainy conditions.
 
Under continuous rainfall conditions, the all-weather paint prototypes sustained average detection distances at 50-70% of their dry-detection distances, as opposed to 17% for conventional paint with glass beads only.
 
Real-world tryout
Based on the Phase 1 test results, 3M selected one prototype of the all-weather marking to evaluate in Phase 2, in which researchers at North Carolina State University and Ohio University teamed up to conduct tests in active highway work zones. The researchers worked with state highway agencies and municipalities to select five sites, three in North Carolina and two in Ohio. Each site had a minimum of two lanes in each direction, no raised pavement markers, a minimum speed limit of 45 mph and no disruption from nearby traffic signals. They also had a history of multiple rainy days during the construction season.
 
Both the conventional and the prototype all-weather pavement-marking systems were applied in each work zone. Researchers used four measures for their analysis: 
 
Paint retroreflectivity, or the ability to reflect light back to the source;
Rate of lane encroachments, as percentage of vehicles that cross the centerline of a multilane road; 
Lateral lane placement, or the proximity of a vehicle to a lane
line; and
Vehicle travel speed, as an indication of a motorist’s perceived risk while traveling through a work zone. 
 
The research team took retroreflectivity measurements of the conventional and all-weather markings the same day the paints were applied to determine differences in paint application across sites and between paint types at the same site. From the data, the researchers concluded that the all-weather pavement markings were significantly more retroreflective than conventional markings when correctly installed. 
 
“The research team suspects there was some human error during the application process due to the differences in machinery used and experience and comfort of the team in actually applying different paint mixtures,” noted an FHWA report on the project, “All-Weather Paint for Work Zones Field Evaluation in North Carolina and Ohio.” Another possible factor, the team said, was variations in the ability of the paint to shed water because of differences in pavement type or roughness, which were not accounted for in the analysis.
 
Watched on video
Researchers measured lane encroachments and lateral lane placement of vehicles to determine if using the all-weather pavement-marking system improved safety.
 
“It was hypothesized that bright lane markings would enhance the driver’s ability to clearly distinguish lanes on the roadway and make safer driving maneuvers,” the project report said.
 
Researchers used video to obtain data on lane encroachments, which were counted when a vehicle’s tire crossed over a solid pavement striping in a work zone. At one work zone, researchers found that a significantly higher number of lane encroachments occurred at curves with standard paint, while at another the difference in lane encroachment rates was statistically insignificant. At both sites, researchers noted more lane encroachments at the point where drivers exited the work zone, indicating that more attention should be given to work-zone exit curves to minimize the risk of collisions.
 
To record lateral lane placement, or the position of the vehicle in the driving lane, researchers used a video camera mounted in a survey vehicle and distance-measuring sensors. The closer a vehicle is to a lane line, the greater the potential for a sideswipe crash or collision with a pedestrian or fixed object. Again, researchers found that the results of their analysis varied, but more often than not, motorists maintained safer lane placements when traveling along lanes marked with the all-weather paint.
 
The data showed that in one work zone, vehicles traveling through areas marked with the all-weather markings generally were able to maintain a position closer to the center of the lane than those traveling through the section with conventional markings. At another work zone, motorists maintained their position in the center of the lane when traveling the all-weather marking section during daytime and nighttime dry conditions. During nighttime rain conditions, motorists stayed nearly in the center of the lane for both the all-weather and conventional marking sections.
 
Researchers studied the speed of drivers traveling through the test sites to supplement their other tests, although they cautioned that higher or lower speeds through work zones do not necessarily indicate improved safety. Speed data—collected at the test sites using laser speed guns, video or sensors—produced no conclusive evidence that drivers travel faster through work-zone detours delineated with the all-weather pavement-marking system than with standard paint. They did, however, tend to slow down when entering work zones and drive faster as they exited, no matter which type of pavement marking was used.
 
Challenges in the field
Although the work-zone tests generally confirmed the retroreflectivity of the all-weather marking system, they demonstrated the challenge of dealing with the uncontrolled variables that a real-world evaluation presents.
 
“Every work zone is different, with various entrance and exit geometries and ambient lighting conditions,” said Mark Zender of 3M’s Traffic Safety Systems Division. “Add to that a multitude of different vehicles with various headlight geometries and functionality and drivers of all different age groups and varying degrees of attentiveness.”
 
Because researchers were evaluating an all-weather marking system, they had to wait for rain and hope that it would be consistent throughout the study area and last long enough for them to collect meaningful data.
 
“Plus, other things happened that were out of our control, like the time the equipment got struck by lightning, wiping out all the data that had been collected,” Zender said.
 
To read “All-Weather Paint for Work Zones Field Evaluation in North Carolina and Ohio,” FHWA’s report on the Technology Partnerships project to refine and evaluate the 3M pavement-marking system, go to www.fhwa.dot.gov/hfl/partnerships/3m.cfm.
 
For more information on Technology Partnerships, visit www.fhwa.dot.gov/hfl/tech.cfm, or contact Julie Zirlin at 202.366.9105 or [email protected]. ST

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