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Do Rough Roads Hurt Fuel Efficiency?

By February 28, 2020 No Comments

Potholes on streets and highways slow traffic, obviously. But even simple pavement roughness can decrease fuel efficiency and increase greenhouse gases (GHGs).

Often overlooked in the conversation about vehicle fuel efficiency, after discussing everything having to do with vehicle technologies, is the effect of road quality. As should surprise no one, a rougher road causes vehicles to burn more energy. It takes two to tango, so to speak, as even a sweet all-electric ride still has to contend with potholes, cracking, and unevenness of all sorts.

This is a topic studied at major transportation departments at the leading universities with such programs (MIT, Auburn University, University of Illinois, and others), as well as at the Federal Highway Administration (U.S. Department of Transportation). Terms such as roughness, macrotexture, and structural responsiveness are tossed about frequently to delve into this technical topic.

But perhaps the term that best describes the overall impact of less-than-smooth pavement is Pavement Vehicle Interaction, or PVI. It encompasses all kinds of distresses to pavement (fatigue cracking, longitudinal and transverse cracking, edge cracking, viscoplastic deformation/deflection, traction when wet, etc.). Poor PVI has at least three deleterious effects on cars, trucks and drivers: a rattling of vehicles that causes wear damage as well as driver fatigue, and decreased fuel efficiency due to lost energy from pavement anomalies.

It bears noting that heavier vehicles, loaded semi-tractor trailers in particular, are effected by viscoplastic deformation more than lighter vehicles. This is when the road actually bends a bit under the vehicle weight, which happens from some types of road construction more than others. It’s similar to when a pedestrian crosses a creek on a rickety bridge that bounces under the walker’s weight: instead of energy being spent to travel horizontally some is spent in a vertical direction; heavier people would experience greater bounce than lighter people.

How serious is that fuel loss? At least two states have measured it to some degree:

Virginia highway engineering researchers found that PVI caused an excess amount of fuel consumption over a seven-year period, which led to an extra 1 million tons of carbon dioxide emissions. Further, their studies identified how a small percentage of the state’s interstate highway network, 1.3%, was the cause of 10% of CO2 emissions – suggesting important gains can be made by addressing the worst of their roads’ pavement.

The California Department of Transportation employed GPS and radar that penetrates surfaces to study the state’s 50,000 lane-mile system. They found that PVI was responsible for 1% of overall fuel consumption. To the individual driver that may not sound like much, but over five years all vehicles consumed one billion more gallons of fuel due to rough pavement. That’s a lot of gas, a lot of carbon, and even a lot more of other pollution caused by gas-fueled cars (carbon monoxide, sulfur dioxide, nitrogen oxides, ozone, volatile organic compounds, aromatic hydrocarbons, and particulate matter).

This data suggests, given how road quality affects all vehicles – regardless of whether they are traditional internal combustion engines or electric driven – that ensuring better pavement, including that which is pothole-free, offers an environmental as well as financial benefit to motorists and commercial freight haulers.