May 1, 2016
Roof Racks Waste 100 Million Gallons Of Gas Nationwide, Can Cut Mileage By As Much As 25 Percent

A Berkeley Lab study published on Monday revealed that roof racks on cars can cut your gas mileage by as much as 25 percent, costing the country 100 million gallons of gas last year.

Roof racks, used to carry bicycles, skis, canoes, snowboards, surfboards and other accessories on the roof of automobiles, are considered fashionable essentials for outdoor trips, vacations, and weekend getaways. The study, published by Lawrence Berkeley National Laboratory, is the first to look extensively at the nationwide impact of automotive roof racks.

Aerodynamics are to blame, and the poor streamlining of the racks, even when not loaded, causes serious losses in individual gas mileage, up to 25 percent depending on the configuration and how frequently it's fully loaded. Use of the racks requires vehicles to fight against the drag and expend more energy to maintain the same amount of speed. In 2015, drag from roof racks was responsible for 0.8 percent of light-duty vehicles' fuel consumption, equal to the consumption of 100 million gallons of gasoline.

A press release put out by Berkeley Lab puts this into context.
"Use of roof racks requires vehicles to expend more energy due to aerodynamic drag. While there have been studies of their impact on individual vehicles—depending on the configuration, the fuel consumption penalty can be 0 to 25 percent on passenger cars—this is the first study to estimate impacts at the national level. Moreover, use of roof racks is projected to increase given national travel trends."
The analysis by Berkeley researcher Alan Meier, the study's lead author, working with Yuche Chen of the National Renewable Energy Laboratory (NREL), projects the data on fuel consumption into the year 2040, by which times the prevalence of automotive roof racks is estimated to increase by about 200 percent in the United States. The researchers recommend undertaking measures in government policy and technology to counter the fuel penalty. They estimate that implementing policies to minimize unloaded roof racks and more energy-efficient designs for cars and racks could save a cumulative 1.2 billion gallons of gasoline over the next 26 year period.

"A national perspective is still needed to justify policy actions," the authors wrote on Berkeley's site. "For comparison, the additional fuel consumption caused by roof racks is about six times larger than anticipated fuel savings from fuel cell vehicles and 40 percent of anticipated fuel savings from battery electric vehicles in 2040."

SFGate summed up the different factors that account for the range between 0 to 25 percent of lost gas mileage.
"The effect on an individual car's mileage varies based on the type of rack itself, whether it's empty or loaded down with a wind-catching bicycle, as well as the type of car. For example, a highly aerodynamic car like a Prius will see a bigger mileage impact from a rack — even an empty one — than will a car whose shape isn't quite so sleek."
Researchers also note that roof rack usage is on the rise in the U.S., particularly with the popularity of SUVs. With the cumulative savings in fuel consumption, just removing roof racks when they are not in use, or implementing some of the policies discussed, would save more than switching to hydrogen fuel cell cars -- a rather stunning revelation.

Disturbingly, if nothing is changed, the study estimates racks will account for a waste of fuel equivalent to six times the anticipated fuel savings from the use of fuel cell vehicles, and 40 percent of the savings from battery-powered electric vehicles in the year 2040.

"It seems to lend itself to an energy label, like we have with refrigerators and other appliances," Alan Meier said to SFGate. "Consumers should be able to make a little better-informed decision."

[Photo by Bryn Lennon/Getty Images]