Study finds roof racks can raise fuel use by up to 25%
Research shows that roof racks, even when unused, can cut fuel efficiency sharply due to added aerodynamic drag, with a major impact on total petrol consumption.
A study by researchers at Lawrence Berkeley National Laboratory and the National Renewable Energy Laboratory has found that roof racks can increase a car’s fuel consumption by as much as 25 percent. The findings, published in the journal Energy Policy, highlight the aerodynamic penalty of fitting roof racks to passenger vehicles, even when they are not carrying a load.
The study estimates that in 2015, roof racks were responsible for 0.8 percent of all light-duty vehicle fuel consumption in the United States, equivalent to around 100 million gallons of petrol. While roof racks are often associated with outdoor activities and heavy loads, the research shows that the majority of their fuel impact comes from racks left permanently on vehicles, travelling empty most of the time.
Researchers found that the aerodynamic drag created by an unloaded roof rack can be particularly costly at motorway speeds. Because drivers cover four to eight times more distance with empty racks than with loaded ones, the cumulative effect on fuel use is substantial. The study’s authors argue that this overlooked factor is a major contributor to wasted fuel and unnecessary emissions from passenger cars.
The case for better rack design and policy
The researchers suggest that more aerodynamic rack designs, combined with government policy to discourage driving with empty racks, could deliver considerable fuel savings. Their projections indicate that such measures could save up to 1.2 billion gallons of petrol in the US over the next 26 years. This would not only cut costs for drivers but also support national targets for reduced fuel consumption and emissions. For context on broader fuel economy trends, seeglobal fuel economy progress falling short of climate goals.
