CLEAN BUSES A WASTE? STUDY CASTS DOUBT ON MTA FUEL CONVERSION.

Byline: Staff and Wire Services

Buses powered by compressed natural gas - long viewed as the cleanest alternative to diesel buses - are no better for the environment than buses powered by a combination of diesel and electricity, according to a study that could have broad implications for vehicle fleets across the United States.

The study calls into question efforts by the Metropolitan Transportation Authority in Los Angeles to convert much of its fleet to natural-gas buses. Los Angeles and other cities around the country have been converting their fleets under pressure to reduce pollution.

The study, by a group that analyzes vehicle pollution for the federal government, is likely to shift the bus debate at a time when all the leading automakers are pushing ahead with the development of electric-and-fuel hybrid cars and light-duty trucks.

MTA officials acknowledged that natural-gas buses need frequent refueling and service, making low-polluting alternatives extremely attractive. Already, 824 of the MTA's 2,258 buses use natural gas. The agency has ordered 750 more and talks are under way to buy 370 others. The MTA is already the No. 1 user of such buses in North America.

``We have a very aggressive bus replacement program,'' said MTA spokesman Bill Heard. ``We're following the industry very closely on the development of hybrid engines. We hope the industry comes up with something that is both reliable and low pollution.''

In New York City, which has enormous influence on the bus market because of the size of its purchases, officials have resisted natural-gas bus technology, citing huge costs and arguing that hybrids would prove better.

``In our opinion, this confirms what we've been saying about the hybrid electric technology,'' said Lawrence G. Reuter, president of New York City Transit, which runs a fleet of 4,300 buses, the largest in the country, 90 of them powered by natural gas and six now being tested with hybrid electric engines.

Reuter added: ``You will see us moving faster into the hybrid technology field.''

Diesel fuel produces more potentially hazardous pollution, known as particulate matter, than natural gas. But the study found that some diesel-electric hybrid engines were built in a way that made the release of such pollution no greater than that given off by natural-gas engines.

However, environmental advocates who have pushed for natural-gas buses immediately criticized the study, saying that while it might show that natural-gas and hybrid buses can produce comparably low levels of the particulate matter, it did not analyze the toxic qualities of those tiny particles.

Some scientific evidence suggests that tiny diesel particles, unlike those from natural-gas engines, can worsen asthma.

The diesel particles have also been listed as a possible carcinogen by the California Air Resources Board, though other groups have disputed this finding. ``It's impossible for us to accept the notion of a clean diesel without knowing the toxicity,'' said Richard Kassel, a senior lawyer for the Natural Resources Defense Council.

As the debate over cleaner buses has played out over the past decade, New York has been the only city in the nation to put a significant amount of money into hybrid diesel technology for its bus fleet.

A large part of the reason is that while natural-gas buses are now cheaper to buy than hybrid buses, it can cost anywhere from $25 million to $40 million to convert a city bus depot so that it can refuel and service natural-gas buses safely.

Six hybrid buses - propelled by electric motors that draw their current from a small diesel engine on board - are being tested by New York, which has ordered 125 more.

The only other cities expressing an interest in the hybrid buses are Tempe, Ariz., and Boston, said Sheila Lynch, executive director of the Northeast Alternative Vehicle Consortium, the nonprofit agency that oversaw the bus tests.

About 30 municipal bus agencies - including those in Los Angeles, Atlanta, Sacramento and Cleveland and the New York Metropolitan Transportation Authority's Long Island fleet - are now buying only compressed-natural-gas buses.

But Lynch said that if the study prompted New York City to move faster into testing and buying hybrid buses, other cities could follow suit and push down the costs of producing them. A hybrid bus costs about $385,000 and a natural-gas bus is about $325,000.

The bus tests, conducted over the spring and fall of last year in Boston and Brooklyn, found that diesel-hybrid buses equipped with pollution-exhaust traps and using special low-sulfur fuel produced so little particle pollution that it could not be detected by engineers' machines.

The hybrid buses, however, produced more nitrogen oxide, which contributes to ground-level ozone. The natural-gas buses also produced too little particle pollution to be detected, though they produced more carbon dioxide, a significant greenhouse gas.

Thomas Balon, a senior project manager for M.J. Bradley, an environmental consulting company that performed the tests, said the particles produced by both the natural-gas bus and the hybrid bus would add up to probably less than a pound a year per bus, compared with as much as 42 pounds per year from a traditional diesel bus.

Advocates of natural-gas buses said they considered the study to be further flawed because the hybrid buses being tested on New York City streets do not use the low-sulfur fuel that was used in the study.

They noted that the low-sulfur fuel is not widely available in the United States. But Reuter, the New York City Transit president, said the agency has begun testing the low-sulfur fuel and that if the tests prove successful, the city will try to persuade fuel companies to produce and sell it.

This story was based on a New York Times report with contribution by Staff Writer Lee Condon