Republicans joined Democrats in foisting a $1 billion program that is supposed to spur car sales on to our already massive debt.

"Cash for Clunkers" will give consumers who trade in a gas guzzler for a more efficient model thousands of dollars in vouchers. Kendra Marr of the Washington Post explains:

The auto sales program, which offers vouchers of up to $4,5000, now moves to the White House for the president's signature. President Obama has repeatedly encouraged Congress to pass a so-called cash-for-clunkers bill. Consumers would be able to start using the vouchers as soon as the National Highway Traffic Safety Administration finalizes the rules -- a process that must conclude within 30 days of the president's approval.

Under the program, trade-in vehicles, 1984 models or newer, must have average fuel economy of no more than 18 miles per gallon. And the new car or truck must get better gas mileage than the one that was scrapped.

The payoff grows depending on the difference in the fuel efficiencies of the old and new cars. For instance, a new car getting at least 4 more miles per gallon than the old car will be eligible for a $3,500 voucher. A new car getting at least 10 more miles per gallon would get a $4,500 voucher.

To guarantee vehicles are actually roadworthy -- and not just sitting on cinder blocks -- trade-ins must be registered and insured to the same owner for at least a year.