Among the many apparent differences between Automated Vehicles (AVs) and human driven vehicles, one of the most significant is how AVs position themselves within a traffic lane. In other words, how do they stay in the lane safely?
AVs are equipped with advanced positioning systems that can keep their position in the lane more precisely than regular, human driven vehicles. Unfortunately, this precise and singular path, which may seem to be the safest solution, can also cause more damage to pavements in terms of cracking and rutting—thus resulting in an increase in the dangerous potential of hydroplaning. This is due to a normal phenomenon called “lateral wandering” that all vehicles experience. Simply put, the less variance in tire contact location and frequency across the horizontal width of the lane, the quicker a rut, which easily fills with water, forms and presents the hydroplaning possibility.
TTI researchers, working under the sponsorship of the Safety Through Disruption (SAFE-D) University Transportation Center, recently examined this issue and presented findings at the 2019 Annual Transportation Research Board (TRB) meeting. The TRB paper, soon to be published, first discusses the technologies, such as machine vision-based and Global Position System-based, with the main objective to keep the AV within the lane with minimum deviation from the center. The measured AV lateral wandering data gathered during the research efforts is also presented.
“We used the data to quantify the negative impact of AVs on pavement cracking and rutting,” says lead researcher Fujie Zhou. “Our findings show that AVs wander laterally at least three times narrower than human driven vehicles.”
How does this narrow wandering of AVs influence pavement rutting and fatigue life? The research analysis showed that it shortens pavement fatigue life by 20 percent and increases pavement rut depth by 30 percent earlier when compared to human operated traffic.
“And it’s the deeper rut depth that leads to higher risk of hydroplaning for all vehicles in all conditions,” says Safe-D Associate Director Sue Chrysler. The research team estimated critical rut depths corresponding to different hydroplaning speeds of AVs under various pavement cross slopes.
The study concluded with a proposed uniformly distributed lateral wandering pattern for AVs that would prolong pavement life and improve roadway safety. Additionally, researchers recommend that to maximize the positive benefit of AVs, current pavement lane width should be kept the same, if not expanded, so that AVs have enough space for more normal, human-like lateral wandering.