Here's an encouraging sign – or rather, billboard: Cruise down the 405 Freeway in El Segundo, California and you'll see a giant billboard with a panel of numbers clicking forward every four seconds, approximating the millions of gallons of gas that have been saved in the U.S. since 2000 thanks to the Toyota Prius and Lexus RX 400h SUV – hybrid-engine vehicles that are selling like hotcakes in America.