California's insurance commissioner has proposed a pay-as-you-drive car insurance option that could reduce premiums as well as greenhouse gas emissions, an idea that makes so much sense that even a caveman ... well, you get the idea.

Under Steve Poizner's proposal, the state would alter its regulations and allow insurers to offer the pay-as-you-drive coverage. Currently, the state requires rates to be based on estimated annual mileage. Officials estimate that if 30 percent of California's drivers opt for the voluntary coverage, the state would reduce CO2 emissions by 55 million tons between 2009 and 2020, or roughly the equivalent of taking 10 million cars off the road.

The proposal is one that's already been endorsed by the Brookings Institution, which estimated in a July report that nationwide pay-as-you-drive insurance would reduce total driving miles by 8 percent, CO2 emissions by 2 percent and oil consumption by about 4 percent. The study also estimated that two-thirds of U.S. households would save money under such a system, paying an average of $270 less per car each year.

"These regulations offer California drivers the chance to base their insurance rates on their actual driving experience," said Roger Wildermuth, a spokesman for USAA, a large insurance provider.

The California proposal, which has been endorsed by the state's Air Resources Board, is currently in the public comment phase. After the process is complete, officials have said the new rules could take effect by the end of next year.