I am currently trying to market an idea that will improve the fuel economy of large trucks by 1-2 miles per gallon.
On the back of my trailer is an unseen fixture which creates a streamlining of its wake vortex, significantly reducing the overall drag. For example, my above SAAB would use 11.5 l/100km (20.4mpg) on 110kph trips around Australia driving the car alone. While pulling the above trailer loaded, weighing 750kg (1650lbs) at the same speeds my fuel consumption would drop to 10.5 l/100km (22.4mpg). That’s an increase of 2mpg while adding an axle and a load.
As applied to a typical “box” style trailer or truck, this device can be manufactured inexpensively from injection molded plastic and applied to the vehicle in under an hour with nothing more than typical hardware and folds out of the way in just seconds for dock operations.