A year ago, Kings County's buses were synonymous with thick plumes of black diesel smoke that often choked drivers traveling behind them. Today, that's mostly an image of the past -- thanks to a new fleet of clean-air buses introduced this summer to replace polluters. The Kings County Area Public Transit Agency is in the process of replacing diesel buses with buses that use compressed natural gas, or CNG, which burns cleaner and costs less than diesel.

Among its fleet of 13 buses that serve fixed routes that currently meander through Kings County are eight CNG buses the agency has recently purchased using federal and state funds totaling nearly $3 million.

One more CNG bus is on order; two more will be added to the fleet by next summer, said Ron Hughes, director of the inter-governmental agency created eight years ago.

"It's a mandate from the California Air Resources Board. We're on the path that has us replacing those buses whether we like it or not," Hughes said. "The other problem is that they no longer make parts for the old diesel buses, so we're at a point where we have to move to another platform ... The change is critical."

The Valley ranks among the nation's dirtiest air basins.

Experts say such a technological conversion motivated by diesel emission reduction is a critical step toward improving air quality, decreasing greenhouse gas emissions and reducing dependence on foreign oil.

From Kings County's point of view, it's all that plus a side benefit: significant cost savings in the operation of a money-losing enterprise mostly supported by tax dollars.

CNG buses aren't cheap. One CNG bus costs $365,000. But long-term benefits far outweigh the cost, Hughes said.

"We end up with much cleaner air, something that has current technology in it, something that has more liability and something that's easier for customers to use," Hughes said.

Replacement of the fleet for the Kings Area Rural Transit bus program, better known as KART, will significantly reduce vehicle exhaust emissions. New buses are six times cleaner than the ones replaced, Hughes said.

Based on data provided by the KCAPTA, CNG is estimated to cost about 45 percent less than diesel.

As of this week, utilities charge about $1.90 per therm (100 cubic feet) for CNG used as a motor fuel, according to the California Energy Commission. That's comparable to paying about $2.20 per diesel equivalent gallon (135.3 cubic feet), and that's also the figure given by Hughes. Diesel today costs about $4 per gallon.

In addition, the new buses get 60 to 80 percent better fuel economy than diesel buses, Hughes said.

With everything considered, the CNG conversion could save his agency about $200,000 a year just on fuel, Hughes said.

The agency also anticipates saving even more on maintenance because the new vehicles come with a warranty. Saving on maintenance on eight CNG buses could amount to $120,000 a year, Hughes said.

The new CNG buses are low-floor buses equipped with ramps that flop out. Unlike the old buses, they have no wheelchair lifts. The new buses are also equipped with eight surveillance cameras inside, ensuring better security.

Feedback from the riders has been positive, Hughes said.

"People love them," Hughes said. "We had City Councilman Dan Chin on a bus at the inauguration of the new transfer site. He commented that this is the best thing he's seen in his travel on buses in terms of the ease to get on it."

Chin is wheelchair-bound.

Also, the new buses are designed so that elderly riders with walkers can simply scoot right in.

"Our older riders -- who would have previously had to get on a dial-a-ride bus, which takes scheduling and wait for the bus -- can now ride that large bus as easily as anyone else can because there's no steps on it," Hughes said.

The reporter can be reached at 583-2429.