Sustainability is an overriding philosophy at Wal-Mart Stores these days, affecting everything from the goods it stocks, how it builds its stores, and especially its truck fleet.

“We are working to build a sustainable company in ways that are driven by our business and are good for our business,” said Leslie Dach, exec. vp of corporate affairs and government relations at Wal-Mart, during a speech earlier this year before the National Retail Federation.

“Traditionally, people around the world have looked to government to solve big problems,” he noted. “But as someone who has worked in politics and business, I can tell you that's changing. People … see business as more results-oriented and performance-based.”

That's especially true when it comes to improving fuel efficiency and lowering pollution from commercial trucks. The company's stated goal is to make its tractor-trailer fleet 50% more energy efficient by 2015 — an effort that should also keep 26 billion lbs. of carbon dioxide out of the air between now and 2020.

To reach that target, Wal-Mart is supporting a number of exclusive projects with truck OEMs and component suppliers — in particular, testing tractors powered by liquefied natural gas along with the development of a diesel-electric hybrid Class 8 truck.

Peterbilt Motors Co. and Westport Innovations are providing four LNG-powered Model 386 tractors that Wal-Mart plans to operate at its Apple Valley, CA, distribution center: a project funded in part by the Mojave Desert Air Quality Management District.

These LNG tractors are powered by a Cummins ISX engine rated at 400 to 450 hp., cranking out 1,750 lbs.-ft. of torque, and will be eligible for a federal tax credit and other state-specific emissions credits. Landon Sproull, chief engineer for Peterbilt, says for these trucks to run on natural gas, the injectors in the Cummins ISX engine are replaced with Westport's High Pressure Direct Injection (HPDI) units.

The HPDI units are able to separately and independently meter, time, then inject both diesel and highly pressurized natural gas directly into the combustion chamber. A small diesel pilot injection is used at all times to provide an initial combustion source, with the majority of the fuel energy delivered through the natural gas injection.

Wal-Mart is also supporting an exclusive joint venture formed by Peterbilt's parent company, Paccar Inc., and component supplier Eaton Corp. to develop a production-ready Class 8 hybrid tractor by 2009 — an effort that is now transitioning into a “second generation” test vehicle.

“Our first task was to just get all the components on there — the electric motor, battery pack and transmission — to show it could work and handle the duty cycle,” Peterbilt's Sproull says. “Now we're moving into the second generation of this technology, where we are trying to refine the entire package to improve overall efficiency.”

For example, Bill Kahn, Peterbilt's hybrid project manager, says the diesel fuel capacity on the Model 386 tractor used as the base chassis for Peterbilt's part of the hybrid project (its sister company, Kenworth Truck Co., also has a tractor involved) has been reduced 15% as a result of the fuel economy gains demonstrated so far.

Currently, Peterbilt's hybrid Model 386 is equipped with a Cummins ISX 400 hp. engine married to an Eaton traction motor and Fuller UltraShift 10-speed automated transmission, along with four lithium ion batteries mounted on the back of the cab. The project goal is to use electric power not only to aid on-road operation but also to provide cooling, heat and hotel loads without idling the engine, says Sproull.