Freightliner says its new Cascadia truck gets 8% better fuel efficiency through such things as hubcap covers and door seals that cut down on wind resistance. The average big rig travels less than 7 miles on a gallon of diesel fuel, making it one of the least-efficient vehicles on the road. Truck manufacturers want to change that. Spurred by new pollution regulations and sluggish demand, truck makers including Navistar International Corp. NAV 0.32% , Daimler AG DMLRY 0.49% , Paccar Inc. PCAR -0.18% and Volvo VOLVB 1.94% AB, along with engine manufacturer Cummins Inc., CMI -0.44% are rethinking everything from engine design to the shape of the trailer to bump up fuel efficiency. Even small gains can have a big environmental impact. Each year in the U.S., roughly 1.7 million tractor-trailer trucks consume about 26 billion gallons of diesel. Getting an extra mile a gallon would equal removing more […]