Retroreflective pavement markings such as bike lane indicators, crosswalks, and lane lines are designed to increase safety. However, the same retroreflective properties that add nighttime visibility can also make them slippery for vulnerable road users such as pedestrians, bicyclists, and motorcyclists—especially in wet or icy conditions.
In recent years, new products that add friction to pavement markings and colored pavements have emerged. Now, U of M researchers and the Minnesota Department of Transportation (MnDOT) are studying these materials to determine whether they can increase the skid resistance of pavement markings in Minnesota. In a CTS webinar on November 8, researchers discussed the project and their preliminary findings.
“There is currently a gap in our understanding of what happens in the transition from a normal pavement surface to a special surface such as marked or colored pavements, and we wanted to address this gap and offer solutions for this issue,” said Mihai Marasteanu, a professor with the Department of Civil, Environmental, and Geo- Engineering.
The researchers started by examining and collecting data to determine the scope of the problem. While they found that the data on crashes caused by slippery pavement markings was limited, a survey of cyclists, motorcyclists, and pedestrians in Minnesota revealed that many of these vulnerable road users had slipped, seen someone slip, or noticed changes in friction when transitioning to pavement markings, particularly in wet or icy conditions. Their research also looked closely at the NordicCert Certification System, a program used by a group of Scandinavian countries that includes friction as a performance measurement.
“A lot of research focuses on the retroreflectivity of pavement markings, but this program was one of the few that incorporated friction measurements,” Marasteanu said. “We think this system could be used to develop something similar or maybe even better for our conditions in Minnesota.”
Next, researchers conducted preliminary testing to determine the best methods for the friction testing of pavement markings. Then, they partnered with MnDOT to evaluate products for skid resistance and durability. At the MnDOT MnROAD test facility, they added 10 different product combinations to their test road in 2-foot by 24-foot swaths. One side of each section will experience traffic and one side will only be plowed; the sections will be measured for skid resistance and checked for durability.
“We wanted to help establish material specification for pavement messages and colored pavements revolving around skid resistance,” said Ethan Peterson, MnDOT’s pavement marking and crashworthy engineer. “Within the last few years we have introduced skid-resistant markings with aggregate, but we’re still not sure what level we should be installing these to.”
Local transportation agencies such as the City of Woodbury expect the findings from this research will help it better incorporate skid resistance into its design guidelines and transportation plans.
“In the past we have really focused on the durability of pavement markings, but we do hear concerns from pedestrians and bicyclists about the skid resistance of our pavement markings, particularly during turning movements,” said Tony Kutzke, city engineer with the City of Woodbury. “We update our specification manual on an annual basis, and we anticipate this research will allow us to take a closer look at our pavement marking guidelines and include skid resistance in our materials selection criteria.”
—Megan Tsai, contributing writer
