Proposition 10 asks voters to borrow $5 billion to help companies and consumers buy environmentally friendly vehicles.

HISTORY

California has long led the nation in the development of alternative fuels such as natural gas, which burns cleaner and produces lower amounts of climate-altering emissions than gasoline or diesel. Vehicle exhaust accounts for nearly 40 percent of California's contribution to global warming. Proposition 10 made the ballot largely because of financial backing from Texas oil and gas man T. Boone Pickens.

WHAT IT WOULD DO

• Authorizes $5 billion in bonds, about $2.9 billion of which would go toward rebates of $2,000 to $50,000 for buyers of alternatively fueled or highly fuel-efficient (at least 45 miles per gallon, highway) vehicles, such as the hybrid Toyota Prius. The largest subsidies would go toward purchase of commercial vehicles and buses powered exclusively by "clean alternative fuels" ­ effectively, natural gas.

• Authorizes $2.1 billion for research, development and training for companies, local governments and colleges for renewable and alternative energy projects.

• Requires the money to be spent within 10 years, with no more than 1 percent for administering the program.

WHAT IT WOULD COST

• With interest charges over 30 years, taxpayers' total cost for the $5 billion bond would be $10 billion, or about $335 million a year, according to the Legislative Analyst's Office.

• The measure also could increase state sales tax revenues potentially tens of millions of dollars in the next 10 years. The amount would depend on the extent to which businesses and individuals use the rebates on vehicles that are more expensive than they would otherwise buy or lease.

SUPPORTERS

• T. Boone Pickens, a director and the majority shareholder of Clean Energy Fuels Corp. of Seal Beach, Calif., the nation's largest supplier of natural gas for fleets of vehicles, including Sacramento city and county garbage trucks and Oakland airport shuttle buses.

• Aubrey McClendon, chief executive of Chesapeake Energy of Oklahoma City, one of the largest natural gas producers in the country.

• David Demers, chief executive of Westport Fuel Systems Inc., a Vancouver, British Columbia, company that makes equipment for natural gas-powered heavy-duty trucks.

WHAT THEY SAY

• The alternative-fuel vehicle rebates would lead to reduced dependence on foreign oil, better air quality and the creation of thousands of clean-energy technology jobs.

• The new vehicle subsidies also would spur owners of truck and bus fleets to retire older, high-polluting diesel rigs sooner than they otherwise would.

• The grant money for development of renewable energy technologies would have utilities generating more electricity from non-oil sources such as solar panels and wind turbines.

OPPONENTS

• Consumer Federation of California

• The Sierra Club

• California Chamber of Commerce

WHAT THEY SAY

• The measure is a costly, self-serving initiative that uses public bond financing, the repayment of which will outlive the natural gas-fueled vehicles.

• The largest beneficiary would be Pickens, whose company would supply most of the fuel for a growing fleet of commercial vehicles and buses that run on natural gas.

• Truck or car buyers who get rebates would not be required to junk their older, dirtier vehicles or to keep the new cleaner-running autos in California.

MONEY WATCH

Proposition 10 is financed heavily by T. Boone Pickens, who has given about $8.8 million of the $11.5 million raised as of Tuesday. Aubrey McClendon's Chesapeake Energy has chipped in $2.5 million. Opponents have raised $60,000.

Source: California Energy Commission, California Department of Motor Vehicles