It's one of the biggest fleets in the world, operating over 219,000 vehicles and logging more than 1.2 billion mi. in 2007 alone. Yet that doesn't deter the U.S. Postal Service (USPS) from seeking ways to improve operations — most notably by exploring alternatives to help reduce its consumption of petroleum-based fuels.

This is because petroleum represents a huge portion of the energy it consumes. According to the USPS, energy use amounted to $2.35 billion in 2007, with transportation representing 75% of that bill. The USPS delivers to 148 million addresses each day, and its outreach grows by almost two million delivery points per year, making continued reductions in fuel consumption a top priority.

USPS is trying to optimize the number of vehicles needed by seeking out the best value in contract transportation to reduce miles and better manage fuel usage. The agency is also exploring the wider use of alternative fuels, from natural gas and propane to hybrid-electric vehicles.

“We are looking for vehicles that operate from a fuel source that reduces, or eliminates, our dependence on petroleum products; [ones] that are good for the environment, good for our customers, and good for the Postal Service,” says Walter O'Tormey, USPS vp-engineering.

“Moving forward with non-petroleum fueled vehicles is more important than ever, since a one-cent increase in a gallon of fuel adds $8 million annually to USPS expenses,” he adds. “Fuel costs last year were $1.7 billion and are expected to increase this year by $600 million.”

The Postal Service operates the nation's largest alternative fuel-capable fleet, some 43,000 vehicles, that can operate on electricity, compressed natural gas, liquid propane gas, E85 ethanol (a mixture of 85% ethanol with 15% gasoline), biodiesel, and fuel cells powered by hydrogen gas.

O'Tormey notes that the USPS has 36,000 E85 flex-fuel vehicles that can operate on gasoline, E85, or any mixture of the two fuels, and it continues to work with the Dept. of Energy's National Renewable Energy Laboratory (NREL) and Clean Cities Program to determine the best places to put E85 vehicles.

The USPS's use of biodiesel is expected to rise in coming years due to future prospects of lower fuel costs and readily available commercial refueling infrastructure. Research partnerships with the NREL continue to expand practical knowledge in using biodiesel, allowing shared experiences with manufacturers, the biodiesel industry, and the general public.

Hybrid vehicles are also being tested for more energy-efficient mail delivery, an effort that currently includes testing 10 Ford Escape Hybrid vehicles in actual delivery situations in Los Angeles and San Francisco, with ongoing plans to convert a two-ton van into a parallel hybrid vehicle for field trials.

Finally, there are hydrogen-powered fuel cells. Since 2004, USPS has partnered with General Motors to explore the applicability of fuel cell vehicles. In July, USPS began testing a Chevrolet Equinox Fuel Cell vehicle in mail-delivery applications.

O'Tormey notes that a hydrogen fuel cell vehicle is twice as efficient as an internal combustion engine and is unique in that the fuel cell emits only water vapor. Hydrogen's greatest advantage is that it can be made in many ways using both traditional and renewable energy sources, such as wind, solar and biomass energy, he says.

“We are very encouraged by GM's fuel cell technology,” O'Tormey stresses. “But we will also continue to explore other options, such as hybrid electric, plug-in hybrid and other green vehicles that will help us continue to provide our customers with reliable service while protecting the environment.”