Tokyo Gov. Shintaro Ishihara is proving to be a man of his word — up to a point. It remains to be seen whether or not he can keep some of his promises. Not long after announcing plans to seriously tackle the capital region’s notorious traffic congestion, Mr. Ishihara and the Tokyo Metropolitan Government are now taking aim at highly pollutant diesel-powered vehicles. The governor has even vowed to “oust” diesel vehicles from Tokyo’s roads. The metropolitan government is reported to be already asking automobile dealers in the capital to refrain from buying or selling diesel-powered passenger vehicles, an easy enough request to meet since there is so little demand for them.

It is diesel-powered trucks and buses, not passenger cars, that are responsible for much of the capital’s air pollution. The metropolitan government estimates that the distance traveled by diesel-powered vehicles accounts for 20 percent of the total travel of all vehicles, but that their engines are responsible for 70 percent of the nitrogen oxides emitted by vehicles. Very few of these vehicles are passenger cars. The governor seems to have grasped the distinction. At a meeting with 160 Tokyo residents, he bravely addressed the question of whether cars “are worth the convenience,” but concentrated mainly on the issue of ridding the capital of diesel-engine trucks.The diesel engine — the most widely used power source for military equipment on both sides during World War II — is today the standard engine for most railroad locomotives, construction and farm machines and large numbers of truck and buses. It has never proved popular for passenger vehicles, however, because of its high vibration rate and the limits it imposes on speed.

Some 650,000 diesel-powered vehicles, 16 percent of the total for the entire nation, are registered in Tokyo. Only 10 percent of the some 3 million vehicles that are on the capital area’s roads every day, however, are estimated to be diesel-powered. But that is enough for sufferers from asthma and other respiratory ailments to welcome the metropolitan government’s intention to do something about the problem, beginning by replacing the 40 diesel-powered vehicles it owns with gasoline-engine ones.

In addition to plans to limit the access of diesel vehicles to government buildings, the metropolitan government is said to be considering enacting an ordinance to promote the general replacement of diesel vehicles with gasoline-powered ones and will work with financial institutions to offer incentives in the form of low-interest loans to vehicle owners who do so. Representatives of the nation’s automobile manufacturers and trucking associations operating in the metropolitan region were on hand for the meeting with Mr. Ishihara and, as was to be expected, objected strongly to being singled out as “the enemy” and as the major cause of the capital’s air pollution.

Some confusion on their part is understandable, since the Transportation Ministry and the Environment Agency appear to favor diesel vehicles for their greater fuel efficiency compared to those using gasoline engines, and because they emit less carbon dioxide, one of the greenhouse gases that contribute to global warming. Indeed, while the Tokyo Metropolitan Government is calling for a reversal of the imposition of a lower tax on diesel fuel than on gasoline, the national government is considering lowering the vehicle and other taxes levied on diesel vehicles to encourage their use. Why not, as the metropolitan government suggests, move up the enforcement of new controls on diesel exhausts already scheduled for 2007? The disagreement is hardly academic. Despite high-sounding promises and noble rhetoric, Japan as a nation has done less than its share to reduce greenhouse-gas emissions. At the same time, medical researchers here continue to discover alarming links between the particles in diesel-fuel exhaust and rising rates of asthma in Tokyo, as well as the growing number of nonsmoking-related deaths from lung cancer. Researchers are also studying a possible link between diesel exhaust and rising rates of sterility or reduced sperm counts in Japanese men.

The Tokyo Metropolitan Government surely knows that only some of its proposed moves against diesel engines will succeed. Yet it is hardly possible to dispute Mr. Ishihara’s contention that the health of Tokyo’s residents is the major point at issue. The governor underscored that by carrying into the Tokyo meeting a plastic bottle filled with the black smoke particles emitted by a diesel-engine vehicle that had traveled just 1 km. Some may consider that a mere public relations ploy, but this is no time for name-calling. The Japan Automobile Dealers Association has just announced that truck sales rose in August for the first time in 29 months.

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