Of the more than 15 million vehicles sold in the U.S. in a typical year, those that run on compressed natural gas (CNG) account for less than one-tenth of one percent. For all their virtues, then, CNG vehicles make only a tiny dent in the quest for reduction of dependence on foreign petroleum. Natural gas currently makes the most sense for fleets, such as taxis and buses. Nearly all natural gas is used for heating homes and businesses, industrial applications or electrical power generation.

Shrunken selection, in numbers and geographically
As late as 2004-05, several vehicles ran on natural gas-or were bi-fuel, operating on CNG or gasoline. General Motors offered a dual-fuel Cavalier, plus CNG full-size vans and pickups. Ford produced Crown Victorias and F-150 pickups that ran on natural gas. So several automakers tried CNG, and they abandoned it. Today, Honda's Civic GX is the only production car that runs on CNG. Barely more than a thousand are sold annually to individuals in only two states: California and New York. For a vehicle on sale for a decade, that's a mighty slim sales total.

Limited range hurts practicality
Filled with CNG, a Civic GX will go no more than 200 to 240 miles. Some analysts consider those figures optimistic. Range also depends on how completely the tank is filled, in terms of pressure. Realistically, owners need another car for longer trips, and most California GX owners have an additional vehicle for that purpose.

Inadequate infrastructure
Anyone driving a natural-gas car learns quickly that fuel is hard to find, especially when leaving tightly defined nearby geographic areas. Infrastructure is the primary obstacle. About 1,500 stations nationwide sell natural gas, in contrast to 175,000 that sell gasoline, and only about half of these are open to the public and they're not evenly distributed geographically.

CNG cars cost more to buy and aren't the most frugal with fuel
The EPA gives the Honda Civic GX a fuel-economy estimate equivalent to 24 mpg in city driving and 36 mpg on the highway with its five-speed automatic transmission. Those figures beat most passenger cars, but aren't the most miserly. In comparison, Honda's own Civic Hybrid gets an EPA estimate of 40/45 mpg, and it can be fueled at any gas station. According the Department of Energy, CNG vehicle fuel economy is similar to a comparable gasoline model, as calculated by "gasoline gallon equivalent." As for that $3,000 California rebate, it's likely to disappear at some point when funds run out.

Safety concerns
Some observers worry about highly pressurized gas in the tank and risks when filling. CNG is stored at up to 3,600 pounds per square inch (psi), so the tank must be considerably stronger than a gasoline tank. The National Highway Traffic Safety Administration (NHTSA) requires that CNG storage cylinders be inspected every three years or 36,000 miles. This mean threats or ruptures or leaks are remote, even in a collision. In a compact car like the Civic GX safety is less a concern than the fact the tube-shaped storage tank eats into precious cargo space.

Safety also is an issue for heavier-duty trucks that use LNG (liquefied natural gas). LNG must be cooled to -260 degrees F. Therefore, tanks must be double-walled and vacuum-insulated.

Performance falls short
Just look at the numbers. The Civic GX has a 113-horsepower, 1.8-liter four-cylinder engine, versus 140 hp in regular Civic models. So, don't expect spectacular performance.

Emissions not that much better than gasoline
Reduction in greenhouse-gas emissions isn't as great as one might expect, compared to gasoline. One industry group estimates the reduction at 20 percent, noting that corn-based ethanol provides a comparable improvement. Of course, hydrogen, which emits little more than water vapor, is far cleaner yet.

Natural gas is subject to depletion
We all know that petroleum is a finite resource. One day, it may all be gone. Because natural gas also is a fossil fuel, the amount in the earth is similarly limited. It's not a renewable fuel, like ethanol. Some analysts believe the total amount of proven natural gas reserves in the U.S. isn't much greater than 200 trillion cubic feet. That means we could run out in a decade or so. Others believe the amount available is six or seven times that figure. Whoever is correct, there is a limit.


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