Courtesy Chrysler Group LLC
A steel box encloses two steel pressurized tanks on the Ram 2500 Heavy Duty CNG, which can haul 1,580 lb in the bed and tow up to 7,650 lb. Ram claims it is the first factory-made truck to run on CNG and gasoline.

The so-called green truck segment is growing fast. By the end of this year, the number of alternative-fuel commercial vehicles on the road in the U.S. is expected to rise to more than 150,000, a 16% annual increase, estimates the National Truck Equipment Association. Although this represents a fraction of the millions of vehicles on the road today, the new breed of trucks is attracting the interest of cost-conscious fleet managers.

Responding to demands for cheaper, cleaner fuels than gasoline or diesel, Ford, General Motors and Ram have introduced new pickups that are designed to run on compressed natural gas (CNG) and gasoline. The "bifuel" trucks debuted at the Work Truck Show, which NTEA hosted on March 6-8 in Indianapolis. Helping to spur adoption and lessen fears, the truck makers are offering standard warranty packages. The models promise a two- to three-year payback, they said.

CNG currently represents the largest volume within the green truck segment, with an estimated 74,000 vehicles on the road this year, says NTEA. Speaking at the Work Truck Show's Green Truck Summit, U.S. Dept. of Energy Secretary Steven Chu called natural gas a "no-brainer" but warned that fuel storage and infrastructure are the limiting factors to widespread adoption.

"The most expensive part is the additional tank," said Chu. "That's the issue."

As for fueling infrastructure, industry experts say CNG works well for short-distance hauls when drivers return each day to a central refueling yard. Many long-haul fleets are considering liquified natural gas, which is denser than CNG and provides more range. The problem? Few truck stops offer LNG pumps.

"CNG trucks are well suited to the severe service market as the payback period can be a little longer," said Ann Duignan, an analyst for J.P. Morgan, in a recent investor note, adding that "some conversions cost up to $18,000, and fleets are balking at this incremental cost."

In the light-duty commercial segment, manufacturers are trying to bring down the added cost, and one strategy is to build the systems in-house. Chrysler's Ram division unveiled what it is calling the first factory-built CNG pickup, which has a range of 255 miles on natural gas and an additional 112 miles on gasoline. Built in Saltillo, Mexico, the 2012 Ram 2500 Heavy Duty CNG—priced at $47,500, or roughly 30% more than a comparably equipped three-quarter-ton Ram—is offered only in a crew-cab, long-box configuration with four-wheel drive. However, it can be had with either standard or medium-level trim packages.

"We have an abundant supply of compressed natural gas here in the U.S., and we intend to use it with this truck," said Fred Diaz, Ram's president and CEO, at the truck show. "It's also a near-term viable option for lessening this country's dependence on crude oil."

The Ram starts on gasoline, then switches automatically to CNG shortly after start-up or when the truck's computer senses a light load on the engine. During a brief test drive, we found the switch to be almost imperceptible. The only indication was an LCD display that changed to "CNG" from "GAS." When the CNG tank is empty, the Ram will automatically switch back to gasoline.

A 5.7-liter HEMI V-8 engine, fitted with hardened valves and seats, supplies power. The bifuel truck comes with a five-year, 100,000-mile warranty, and its two CNG tanks, which rest in a steel box mounted flush with the top of the bed, are covered under a three-year, 36,000-mile warranty. Ram is taking fleet orders now for summer delivery.