Study Aims to Update Highway Curves for Modern Vehicles

Electric vehicles often carry hundreds of pounds of batteries beneath their cabin, changing their weight distribution and center of gravity. Combined with advancements in tires, changes in suspension systems and electronic stability controls, those differences can change how modern vehicles navigate curves.

"Changes in vehicle weight, weight distribution, tires and other vehicle technologies can affect how a vehicle behaves on a curve," said Amir Molan, Ole Miss assistant professor of civil engineering. "The sliding and skidding potential can be different.

"We want to understand how well the existing design criteria work with today's vehicles and whether any changes are needed."

Molan and engineering graduate students Shaishav Acharya and Jawad Mehmood are conducting the research under a $500,000 contract from the National Cooperative Highway Research Program which is administered by the Transportation Research Board of the National Academies of Sciences, Engineering and Medicine. The study will examine how the banking of curves on America's highways – known as superelevation – performs for modern vehicles.

"When you are moving through a horizontal curve, there are a lot of forces acting on the vehicle, and those forces can cause the vehicle to skid or roll over," Mehmood said. "We now have advanced tires, advanced pavements and automated and electric vehicles, so that has changed the dynamics of rollovers and skidding.

"We want to analyze these modern changes and test how vehicles perform on curves."

Many electric vehicles are heavier than comparable gas-powered vehicles because of their batteries, which are often located on the underside of the car.

"That could actually help the stability of the vehicle," Acharya said. "As the center of gravity moves downward, the stability of the vehicle improves.

"That's different from many conventional vehicles, and these are factors that may not be fully reflected in existing guidelines."

Curves still need to accommodate older vehicles that remain in use across the country, Molan said. The goal of the project is to provide guidance needed to make roads safer for all travelers, not just those in electric or automated vehicles.

"That is one of the main objectives," he said. "We have to make sure that whatever recommendations we provide are consistent with existing infrastructure and the vehicles we already have."

While most roads will see a mix of newer and older cars, some will see more electric and automated vehicles than others. The Vegas Loop is an underground transportation system in Nevada that uses a fleet of all-electric vehicles to shuttle passengers through tunnels. A similar project is under construction in Nashville.

"If you're dealing with a roadway that is going to be made especially for electric vehicles or automated vehicles, what are some of the considerations that should be added to the infrastructure?" Molan said. "What guidance can we provide regarding speed or design to improve safety?"

The results of the study could help inform future updates to the American Association of State Highway and Transportation Officials' A Policy on Geometric Design of Highways and Streets, also known as the AASHTO Green Book, a widely used national reference for highway and roads design.

"It is perhaps the most well-known road design guideline in the world," Molan said. "Many countries translate the AASHTO Green Book into their own languages."

The researchers will submit their final recommendations for consideration by AASHTO, where the findings could help inform future highway design guidance, Acharya said.

"Vehicles have been changing," he said. "So, we need to make sure the guidelines keep pace with those changes."

This research is being conducted under NCHRP project 15-85.

Top: Many roadway curves were designed with older vehicles in mind. An Ole Miss civil engineering team led by professor Amir Molan is studying whether these roadway designs work for electric and autonomous vehicles, which have different centers of gravity than traditional petroleum-fueled cars and trucks. Photo illustration by Stefanie Goodwiller/University Marketing and Communications