When the open road beckons, drivers can make their road trips more affordable by implementing various strategies to conserve fuel. A study from the Oak Ridge National Laboratory found that rooftop cargo boxes can reduce fuel efficiency by as much as 17 percent on the highway and as much as 25 percent on interstates where drivers drive at speeds between 65 and 75 miles per hour. When the open road beckons, drivers can make their road trips more affordable by implementing various strategies to conserve fuel.