Increasing pavement skid resistance on a London highway by 50% reduced the total number of accidents over four years by 45%, according to the United Kingdom Transport and Road Research Laboratory. The United States National Transportation Safety Board and Federal Highway Administration stated that poor pavement skid resistance is a major cause of driving accidents. These are just two sources cited by an international team of researchers who recently reviewed more than 3,000 studies on tire-road friction and found that while tire-road friction theory and simulations have been well developed across the research scales — rubber-pavement scale, the tire-road scale and the vehicle scale — the scales themselves remain largely unconnected.

According to the researchers, who published their work on Feb. 10 in Friction, that disconnect is a major hindrance in advancing the field, and ultimately, road safety for all. 

“The concept of pavement skid resistance pertains to the capacity of road surfaces to provide adequate friction during diverse vehicular operations, including braking, accelerating and cornering,” said co-corresponding author Yuchuan Du, professor, Key Laboratory of Road and Traffic Engineering, Ministry of Education, Tongji University, China. “It is critical for preventing skidding incidents and ensuring driving safety, serving as a significant indicator for road performance evaluation and maintenance decisions.”

Tire-road friction has been studied for more than half a century, Du said, explaining that early studies focused on improving the materials and structure of the tire. However, researchers later learned that simply improving tires did not reduce the proportion of skidding accidents, so more researchers in the field focused on the skid resistance of the road itself.

“From the perspective of road researchers, the primary concern is the role that the pavement itself plays within the tire-rubber friction system, which is referred to as the pavement skid resistance,” Du said. “This is an inherent characteristic of the pavement within the tire-road friction system, and understanding the tire-road friction system is fundamental for evaluating the skid resistance of asphalt pavements.”

From their analysis of the field’s scientific literature, the researchers found that studies typically fell into one of four research paradigms: experimental science, theoretical science, computational science and data science. They also found that the research can be categorized into the rubber-pavement scale, the tire-road scale and the vehicle scale. Across the paradigms and scales, the team found that experimental studies were limited by specific variables that have made reproducibility difficult, and that computational studies were limited by their ability to integrate friction mechanisms, making them difficult to interpret properly.

“The synergistic development of the four research paradigms can promote and advance the understanding and application of tire-road friction mechanisms,” Du said.

The researchers developed a multiscale architecture for tire-road friction research to clarify the different concepts and boundaries as they feed into two coefficients: rubber-pavement friction and tire-pavement adhesion. Both feed into determining the skidding risk of the vehicle, along with other variables. The two coefficients are determined by pavement factors, such as texture and aggregate; rubber-related material properties, like density; environmental factors, including temperature and humidity; tire-related physical conditions, such as pattern and pressure; and vehicle-related operation conditions, like load and velocity.

“With the accumulation of data, data-based research has gradually become the primary research paradigm for evaluating pavement skid resistance,” Du said. “However, the integration of data with theoretical research remains a question that requires further exploration. Leveraging theory to enhance the predictive capabilities of data models and utilizing data mining to reveal the underlying mechanisms and patterns of pavement skid resistance are areas that warrant deeper investigation.”

Collaborators include Zihang Weng and co-corresponding author Zhen Leng, Department of Civil and Environmental Engineering, Hong Kong Polytechnical University, China; Chenglong Liu and Difei Wu, Key Laboratory of Road and Traffic Engineering, Ministry of Education, Tongji University, China; and Bryan T. Adey, Institute of Construction and Infrastructure Management, Swiss Federal Institute of Technology, Switzerland. Weng is also affiliated with Tongji University and Hong Kong Polytechnic University Shenzhen Research Institute.

The National Natural Science Foundation of China, the Shanghai Science and Technology Innovation Action Plan and the Carbon Neutrality Funding Scheme of PolyU supported this research.