Not only do old cars pollute more than new ones, they pollute a lot more. According to a rule proposed by the California Bureau of Automotive Repair, fully “75 percent of vehicular pollution is caused by just 25 percent of the vehicle fleet" in the state.

Those vehicles were built before 1995, meaning they didn't have to meet emissions standards anywhere as tight as current limits. The state has more than 3 million pre-1995 cars registered, some with failing emissions control systems, many owned by low-income drivers.

Removing these "gross polluters" from the roads when they fail their biannual smog checks (required for cars six years old or more) is one of the most cost-effective ways available to the state to reduce vehicle emissions.

California also offers financial assistance to low-income owners that is restricted to repairs that bring the car into compliance with the emissions limits for its model year.

Now, under proposed rules issued late last month, the state is proposing to expand its Fleet Modernization Program, which currently offers bounties for owners to retire cars that fail their smog checks.

The expanded program would add trucks, sport-utility vehicles, and vans. It would also expand eligibility to more than 10,000 vehicles that are in between smog checks. It would be relatively cheap, as these things go: $12 million in the first year, $14.4 million a year thereafter.

Roughly 22,000 vehicles a year are now scrapped under the program. It operates similarly to last summer's Cash For Clunkers program, which offered bounties for trading in older vehicles with low fuel efficiency for new, higher-mileage ones.

Owners of gross polluters can apply to the Bureau of Auto Repair (BAR) for a letter of approval to scrap the vehicle. When they turn in the vehicle at a BAR-approved dismantler and receive proof that it has been scrapped, they receive a payment of $1,000 to $1,500. Air-quality advocates hope the bounty can be raised to $2,000 per car.

Early retirement programs have long raised fears among car collectors that the state would target collector cars--there's no argument that Sixties muscle cars are highly polluting--but California consistently stresses that the program is voluntary.

No smog checks are required in California for cars built before 1976, when the first catalytic converters were installed on new cars.

Nor are they required for hybrid cars, motorcycles, diesel cars built in 1997 or earlier, large diesel trucks, or cars with two-stroke engines or engines smaller than 0.8 liters.

[EFMP at Taking the Hill via All Car Advice]