WASHINGTON -- When it comes to fuel economy and tailpipe emissions, today's diesel vehicles are as eco-friendly as their gasoline-fueled counterparts, and often more so.
This is real progress. Unlike "clean coal," "clean diesel" is more than a marketing phrase.
Companies such as Volkswagen AG, Chrysler Group and General Motors have invested billions to make that happen, outfitting vehicles with systems that cut tailpipe emissions by about 99 percent from a decade ago. So why would the Washington city government ban the registration of diesel vehicles in the nation's capital in 2018?
To automakers, that seemed to be the intent of a provision buried in an environmental bill that D.C. Mayor Vincent Gray introduced in November. Though the city of 630,000 people has a small car and truck market, it was such an unusual proposal that it drew attention from worried diesel advocates around the country.
"There's nothing in the preamble to the bill that says why they're doing this," said Ezra Finkin, a policy director at the Diesel Technology Forum, a trade group that includes makers of diesel vehicles. "Is this for energy independence? Is this for emissions? Is this for greenhouse gas reduction purposes? We don't know."
It now seems clear that the D.C. government had no intention of banning the new breed of diesels. But the confusion suggests it will be awhile before "clean diesels" can displace dirty old diesels from the roads and from the minds of policymakers.
The provision actually targeted older diesel trucks that belch smoke, or the "legacy fleet," as Karim Marshall, a legislative and regulatory analyst at the District Department of the Environment, put it.
Marshall said the proposal would not apply to vehicles that run partially on biodiesel -- meaning new light-duty vehicles would not be affected, but some old trucks would.
"We know that the technology is evolving," he said.
No one would even suggest a ban on gasoline vehicles, which do their fair share of polluting -- but diesel still has an image problem. That's bad news for those who see it as a fantastic way to cut the United States' oil consumption, air pollution and greenhouse gas emissions.
Many Americans grew up breathing diesel fumes from school buses and have spent decades watching trucks and buses spew smoke.
So no matter how clean the new "clean diesels" are, it is going to be difficult to get equal treatment with hybrids and electric vehicles, which have no such stigma. Brands including VW and Audi are pushing hard for diesel perks such as government tax credits and access to HOV lanes, but as long as misperceptions persist, it's going to be a hard sell.
The drive to clean diesel has always relied on rationality. The thinking is, if you deliver better fuel economy, longer driving range and lower emissions without a drop in performance, customers and the government will pay attention. Diesel may not be as clean as a hybrid or an EV, but it's cleaner than gasoline. Of course, people are not perfectly rational. Neither are their laws.