United Parcel Service is so committed to using low-emissions fuels that all of the 700 Class 8 vehicles it has ordered for delivery late this year and into 2014 will run on liquefied natural gas. The order follows five years and 300 million miles of successful experience with 2,700 trucks and package cars fueled by natural gas, said David Abney, chief operating officer of the giant package carrier and logistics company.

But one of the things UPS managers learned in those 300 million “green” miles is that “the greenest miles are the ones you never run,” he commented. The company uses computerized route planning and a “smart pick-up” system based on communications with customers to avoid needless miles.

“There was a time when we used to stop everywhere every day, even if there were no pick ups” from regular customers, related Abney, who began his career with UPS as a part-time loader and later worked as a route driver. “Those days are gone.” About 364 million miles were saved in 2011 and ’12.

UPS has worked with natural gas since 1989, and now has about 3,000 alternative-fuel trucks among the 90,000 it runs worldwide, Abney told an audience at the Alternative Clean Transportation Expo in Washington, D.C. , on Wednesday morning. In addition to about 1,000 package cars running on compressed natural gas, it also has some on propane, others with diesel-electric hybrids, and still others with electric-drive powertrains.

Altogether, UPS expects to cover 500 million green miles by 2015 and 1 billion by 2017. To help support that, it plans to build nine LNG fueling stations this year and next.

The 700 LNG road tractors will use dual-fuel gas-and-diesel vehicles from Cummins Westport and Kenworth, as well as straight-gas engines, the latter spark-ignited Cummins models in Mack chassis.  These are the first Macks built with Cummins’ ISX12 G engines that are fueled by LNG instead of CNG, a Mack source said.

The Mack order follows a test of one tractor in regular service in Greensboro, N.C., a Mack announcement said. It has been running two 350- to 400-mile shifts per day, pulling single-semi and doubles combinations grossing up to 80,000 pounds. The 11.9-liter ISX12 G is rated at 400 horsepower and 1,450 pounds-feet, which has proven sufficient for such road duty.

Abney said UPS pays about $100,000 extra for a natural-gas-fueled road tractor. That premium is paid off because gas is cheaper than diesel and the tractors run high miles over which high amounts of the cheaper fuel are used.

UPS and other fleets might buy more such vehicles except for the penalty of taxation, he said. Some of those upcharges are the 12% federal excise tax on the extra gas equipment, which he thinks the government should exempt to encourage use of the clean-burning fuel.

And the federal road tax on LNG amounts to 17 cents per gallon extra, because it’s taxed as a liquid, like diesel, even though it has less energy than diesel. LNG should be taxed on its energy content, not its liquid volume, Abney said.