Dear Tom and Ray:

I got my copy of Drive magazine from Subaru today, and they talk about something called PZEV. Apparently, it stands for Partial Zero Emission Vehicle. I've never heard of that. What is it? -- Mary Ann

RAY: Interesting terminology, isn't it? I'm not a mathematician, but I don't think there's any such thing as "partial zero."

TOM: Right. My brother, for instance, has always been a complete zero.

RAY: The real story of the term PZEV involves a lot of letters, Mary Ann. So you'll need to pay attention. It starts with an Environmental Protection Agency emissions standard for cars called LEV, which stood for Low Emissions Vehicle. That standard set limits for how much a car could pollute.

TOM: LEV was eventually replaced by ULEV, or the Ultra Low Emissions Vehicle standard. Then came the current standard, SULEV, for (you guessed it) Super Ultra Low Emissions Vehicle. An SULEV vehicle is supposed to produce 90 percent less emissions than the average vehicle made in 2003. That's pretty good.

RAY: Here, our story moves from the offices of the EPA in Washington, D.C., to the sunny state of California.

TOM: In 2003, California decided that it wanted to use standards that were stricter than the federal government's. So, they mandated that within a decade or so, manufacturers would have to sell 25,000 cars in their state that produced no emissions at all. These would be, presumably, battery- or fuel-cell-powered cars. California called these Zero Emission Vehicles, or ZEVs. Now we're getting warmer, right?

RAY: But there was a lot of whining and threatening of lawsuits from the carmakers, and ultimately, California state regulators backed down and modified their plan. They made drastic cuts in the number of ZEVs required, and instead, they called for more SULEV vehicles, with a couple of additional requirements: that the cars produce no evaporative emissions (from evaporating gasoline), and that the warranty on all emissions components be extended to 15 years or 150,000 miles.

TOM: Now, what do you think California decided to call these enhanced SULEV cars?

RAY: Uh, SDULEV? Super Duper Ultra Low Emission Vehicles?

TOM: No. Think public relations. California regulators didn't want to lose face. They wanted it to appear that they were staying close to their lofty ZEV aspirations. So they called the enhanced SULEVs PZEVs, or Partial Zero Emission Vehicles. And that's where the wacky name comes from.

RAY: Since then, other states have adopted California's emissions standards. We now have PZEVs in some states and SULEVs in others, and, except for a better warranty, they're essentially the same thing. Glad we could clear everything up for you, Mary Ann!