CLICK & CLACK : Partial to Zero

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Sunday, September 7, 2008

Dear Tom and Ray:

I got my copy of Drive magazine from Subaru today, and they talk about a PZEV, which apparently stands for Partial Zero Emission Vehicle. What is that?

-- Mary Ann

RAY: I'm not a mathematician, but I don't think there's any such thing as "partial zero." The story of PZEV involves a lot of letters, Mary Ann. 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. A 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 the District to the sunny state of California.

TOM: In 2003, California decided it wanted to use standards that were tighter than the federal government's. So, it mandated that within a decade or so, manufacturers would have to sell 25,000 cars in the 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.

RAY: But there was a lot of whining and threatening of lawsuits from the carmakers, and ultimately, California state regulators backed down. They made drastic cuts in the number of ZEVs required and instead called for more SULEV vehicles, with 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: 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 standards. We now have PZEVs in some states and SULEVs in others, and, except for a better warranty, they're essentially the same thing.

Dear Tom and Ray:

I heard that turning off the car's air conditioner and opening the window will increase gas mileage and thus save money. But I say opening the windows would increase the drag and therefore reduce your gas mileage. Am I right? -- Sam

RAY: You are right. Using the air conditioner does lower your gas mileage, but not as much as opening the windows does.

TOM: Just to be clear, we're talking about driving at moderate to high speeds. At those speeds, where aerodynamics play a key role in your mileage, you're better off with the windows closed on a modern car.

RAY: When they design cars now, and do wind-tunnel testing or modeling, it's assumed that the windows will be closed, so the sides of the car will be smooth. Otherwise, the airflow around the car is interrupted, and mileage will suffer.

TOM: At lower speeds, it's more of a toss-up. Imagine if you're stopped in traffic or moving at less than 20 miles per hour. Then, aerodynamics is hardly a factor. In that case, turning off the AC and opening the windows WOULD save you more fuel.

RAY: Of course, when you're stopped in traffic and open the window, there's no breeze! So it's not always a good option, despite the energy you'd save.

Got a question about cars? Write to Click & Clack in care of The Post, or e-mail them through http://www.cartalk.com.

Copyright 2007 by Tom and Ray Magliozzi and Doug Berman


© 2008 The Washington Post Company

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