The Green Room

In trucking, the road to efficiency is continuous

By Elizabeth Fretheim on May 3, 2012 Leave a comment

Walmart is continuously working to improve its trucking fleet through technologies like this hybrid assist truck. Since 2007, the Walmart fleet has delivered 361 million more cases while driving 287 million fewer miles.

Delivering more while driving less: It’s a simple idea, but bringing it to life can be a bit complicated.

Walmart U.S. Logistics spends a lot of time developing and testing advanced technologies to improve the efficiency of its trucks. We have built a variety of prototype tractors for testing in a real-life environment. And like with many emerging technologies, these trucks may never enter operation or may not stay there long. We’re testing and piloting as we search for the best answers.

Here’s a look at some of the technologies we’ve worked on so far.

Hybrid assist: Hybrid assist tractors use a traditional diesel drivetrain along with an electric motor to recover energy normally lost during braking. This provides additional torque in high-load situations like going up hills. The onboard batteries are also used to run components such as heating, air conditioning and the electrical system when the engine is off. This model was our first hybrid tractor and was built in partnership with Peterbilt and Eaton Corporation. Over the course of a year, we gathered data and highlighted key areas of opportunity, such as batteries, needed to achieve an acceptable return on investment. Hurdles for the batteries include cost, size and weight and capacity.

Wheel-end hybrid assist: The concept of this hybrid, built in partnership with Freightliner, is similar to the one above, except for the placement of the electric motor. This tractor has two wheel-end motors on the second axle, putting the energy right where it is needed and avoiding energy loss from the front of the tractor. Already under development, the next generation of this tractor will attempt to resolve the inability to add future enhancements, such as stationary recharge of the hybrid battery due to current motor placement.

Full propulsion hybrid: This configuration is a dual-mode hybrid with the ability to run completely on its electric motor when traveling under 48 miles per hour. When it passes that mark, it switches over to a diesel engine. This hybrid, built by Meritor, was the first of its kind in this class when unveiled. Similar to the hybrid assist tractors, the next generation of this hybrid drive system is under development, being paced by the design of a battery system with enhanced performance and improved robustness.

Natural gas: Walmart has been testing five Westport Liquid Natural Gas trucks in California for the past three years, and now also has a Westport/Cummins Alpha 12-liter natural gas engine. This new truck will run on compressed natural gas and will also be tested in California. Available fueling infrastructure is a challenge, and we continue to review the technology performance and potential sustainability benefits.

Technology truck: In our continuing quest for improved efficiency, considerable opportunity lies in improving the individual components of a truck. Walmart and Freightliner have worked together to build an advanced, aerodynamic tractor with the latest in efficiency and predictive technologies. This tractor was built with further development in mind and will be retrofitted with new advancements as they become available.

From the Global Responsibility Report

These and other technologies are moving us toward the goal of doubling our fleet efficiency.

In 2011, we achieved almost 69 percent improvement in fleet efficiency over our 2005 baseline. Throughout our network, we delivered 65 million more cases, while driving 28 million fewer miles, by increasing our pallets per trailer and better managing our routes. That’s the equivalent of taking about 7,900 cars off the road.