Wal-Mart says it intends to double the mpg efficiency of its entire truck fleet within the next decade, and save $52 million/year in the process.

Land Line magazine reports that, beginning with the its 2007 model-year trucks, the retail behemoth will begin introducing trucks with improved aerodynamics, transmission, tires and an auxiliary power unit in every truck in its fleet. By 2015, Wal-Mart expects its entire fleet to reach 13 mpg — about double its current figure, the Associated Press reports.

One of the most visible changes will be wind skirts on the trailers' sides between the axles to reduce wind resistance and airflow around the trailer. Dual tires on the trucks' rear axles will be replaced with extra-wide single tires, and the tractors will be more aerodynamic.