How poor roads hurt consumers and climate
As the summer driving season winds down and motorists rack up big gasoline bills from beach trips and college drop-offs, few people are aware that the quality of our roads impacts the amount of fuel we use. It’s not just potholes either — the smoothness and stiffness of the roads we drive on determines how hard our vehicles have to work to reach their destination — and therefore increases the price we as drivers pay.
The dynamic is called Pavement Vehicle Interaction (PVI) — and it impacts everything from greenhouse gas emissions to our annual budget for gasoline. All vehicles, whether gasoline, diesel or electric, use energy to move — but some of that energy is being wasted. On roads with poor surface conditions or subpar structural properties, vehicles consume more fuel than what’s needed to move. Researchers are now focusing in on that excess fuel consumption by taking a hard look at PVI.
Pavement influences fuel use, greenhouse gas
PVI boils down to three factors — roughness, texture and deflection — all of which combine to determine how much bang you get from the bucks you spend at the gas station. The first component, roughness, relates to how bumpy or smooth the road is. Commonly seen and felt via cracks and potholes, roughness is a big determinant of the performance of passenger vehicles.
The next factor is texture — the abrasiveness of the road surface — which relates to vehicle traction when surface conditions are wet.
The final component is deflection, or the bending of pavement under the weight of a vehicle. This is a big factor for trucks and other heavy vehicles. Deflection is a condition determined by the initial construction of a road, and ultimately depends on pavement design. Think of the difference between walking on sand versus a sidewalk — vehicles work harder when the deflection of a pavement is greater.
Excess fuel consumption and air emissions can be significantly reduced by building stiffer roads and maintaining smoother pavements. Road stiffness is particularly relevant for 40-ton trucks, where research shows that lessening the impacts of deflection could generate up to 4 percent in fuel savings. When you consider the amount of fuel consumed by trucks each year, that 4 percent in savings could quickly add up.
Altogether, 2 million tons of savings in carbon dioxide emissions each year are achievable by addressing road stiffness nationwide. As more efficient hybrid and electric power-trains become increasingly more common — helping to eliminate vehicle engine losses in and of themselves — the role of PVI in the excess energy consumption of trucks could increase to as much as 8 percent.
Data from individual states helps illustrate the real-world impact of PVI. Using data collected by the California Department of Transportation (Caltrans) through the use of GPS and ground-penetrating radar, researchers conducted an analysis of the state’s entire 50,000 lane-mile system, and found that PVI accounted for 1% of overall fuel consumption on California highways. At a scale as vast as the California highway system, that 1% amounted to 1 billion gallons of excess fuel consumption over a five-year period due to PVI factors.
Actions that improve road design and conditions can reduce vehicle fuel consumption and emissions. As well, it becomes an important factor for state officials who should want to improve transportation maintenance, planning and budgeting so taxpayers can get the most effective bang for their transportation buck.
Jeremy Gregory is the executive director of the Concrete Sustainability Hub at the Massachusetts Institute of Technology. Twitter: @jeremyrgregory