On a recent run from Boston to Cape Cod, I test drove the 2008 Honda Accord, the latest version of this family favorite. The new Accord boasts an environmental first: a six-cylinder gasoline engine that's cleaner than many hybrid systems. There's only one catch: You can't actually buy this ultra-green Accord, or the four-cylinder version that also produces near-zero pollution. That is, unless you live in California, New York or six other northeast states that follow California's tougher pollution rules. Only there can you buy this Accord, or the roughly two dozen other models that meet so-called Partial Zero Emissions Vehicle standards, PZEV for short. Not only can't you buy one, but the government says it's currently illegal for automakers to sell these green cars outside of the special states. Under terms of the Clean Air Act - in the kind of delicious irony only our government can pull off - anyone (dealer, consumer, automaker) involved in an out-of-bounds PZEV sale could be subject to civil fines of up to $27,500. Volvo sent its dealers a memo alerting them to this fact, noting that its greenest S40 and V50 models were only for the special states. So, just how green is a PZEV machine? Well, if you just cut your lawn with a gas mower, congratulations, you just put out more pollution in one hour than these cars do in 2,000 miles of driving. Grill a single juicy burger, and you've cooked up the same hydrocarbon emissions as a three-hour drive in a Ford Focus PZEV. As the California Air Resources Board has noted, the tailpipe emissions of these cars can be cleaner than the outside air in smoggy cities. PZEV models are already available from Toyota, Ford, Honda, GM, Subaru, Volvo and VW. But chances are, you've never heard of them.