While nations like Argentina, Pakistan and Brazil all have more than 1.4 million natural gas vehicles on the road, it's been more difficult to increase the U.S. usage numbers because, until recently, oil prices in the U.S. were relatively inexpensive, said David Gelman, the vice president of New West Technologies, who has been involved in the alternative fuel industry since 1985.

"There's no question now that the majority of the applications for natural gas now are still in centralized fleets," Gelman said.

"For us to deal with this issue, everybody has got to change their mind-set that you're going to have one fuel choice. The idea is, you might have five or six. The question is, which one makes sense for which part of the country, which one makes sense for which type of application."

"Natural gas vehicles help achieve three major public policy goals simultaneously," Kolodziej said. "They produce less greenhouse gases, reduce air pollution and displace the use of foreign oil, and CNG is far cheaper than gasoline or diesel fuel."

Vehicle Safety

Natural gas vehicles are just as safe as today's conventional gasoline and diesel vehicles. They use pressurized tanks, which have been designed to withstand severe impact, high external temperatures, and environmental exposure.