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Alabama Water Institute

UA Researchers Find Hydroplaning Risks Greater in Southern US

map of the US showing traffic volume per year

Research from The University of Alabama reveals the southern United States is a primary hotspot for hydroplaning due to extreme rainfall, a phenomenon that is known to elevate the risks of road accidents.

study recently published by Kaustubh Anil Salvi, a postdoctoral researcher with the Alabama Transportation Institute, and Dr. Mukesh Kumar, associate professor of civil, construction and environmental engineering, is the first to map the spatiotemporal distribution of rain-induced hydroplaning on a national scale and detect regions with relatively high risks.

Weather is often a substantial factor in automobile accidents, particularly during rainfall when visibility decreases and ponded water creates reduced friction between the pavement and the tires of a moving vehicle. Other influences include the condition of the pavement and tires, the speed of the vehicles and human factors.

Between 1980 and 2017, approximately 24%, or 200,444 miles, of road within the continental U.S. were at risk of hydroplaning events. Of these, more than 840 miles of the roads experienced five or more of these events per year. Approximately 87% miles of such sections are in southern states, which receive frequent and intense rainstorms. In fact, six of the top 10 states at risk for these hydroplaning events reside in the South – Florida, Texas, Alabama, Oklahoma, Mississippi and Georgia.

Salvi and Kumar found that when coupled with rain, hydroplaning risks increase with wider and larger numbers of highway lanes, and higher speed limits. These conditions are more prevalent in the South than, for example, in the Pacific Northwest where rain is also significant, but roads are slightly narrower and speed limits are slower on average. Narrower roads keep the runoff depth in check.

As climate change continues, the frequency of larger precipitation events is expected to become more intense. That poses a bigger problem for drivers everywhere but especially for those in areas already prone to hydroplaning.

“If the temporal trends of the past 38 years continue into the future, our results show that road sections with large traffic volumes will be disproportionally affected,” said Kumar.

“While locations with frequent risks of hydroplaning will likely catch the attention of planners, road sections experiencing lower risks but with high traffic volumes should also be prioritized for risk mitigation,” added Salvi.

Current designs and engineering of pavement, tires, traffic signs and rules often help reduce the likelihood of hydroplaning and ensure road safety. However, it still occurs when intense rainfall results in the development of thick water film on the pavement. By using the results of this study, Salvi and Kumar believe the data gathered can help decision-makers facilitate targeted and precise mitigation plans to alleviate future risks.