Roof racks on light-duty vehicles in the US were responsible for 0.8‰ (permille, parts per thousand) of light duty vehicle fuel consumption in 2015, corresponding to 100 million gallons of gasoline per year, according to a new study by a duo from the National Renewable Energy Laboratory (NREL) and Lawrence Berkeley National Laboratory. The study is published in the journal Energy Policy.
After-market roof racks are attached to a vehicle for carrying over-sized items, such as bicycles and skis.
The researchers developed a model incorporating real-world data and vehicle stock information to enable assessing fuel consumption impacts for several categories of vehicles, rack configurations, and usage conditions. Their model also draws on two new data-gathering techniques: on-line forums and crowd-sourcing.
Sensitivity analyses showed that results are most sensitive to the fraction of vehicles with installed roof racks but carrying no equipment.
The aerodynamic efficiency of typical roof racks can be greatly improved and reduce individual vehicle fuel consumption; however, government policies to minimize extensive driving with empty racks—if successful—could save more fuel nationally.—Chen and Meier (2016)
Yuche Chen, Alan Meier (2016) “Fuel consumption impacts of auto roof racks,” Energy Policy, Volume 92, Pages 325-333, doi: 10.1016/j.enpol.2016.02.031