SACRAMENTO, Calif. -- Where Highway 99 meets the state capital here, a motorist has choices. He can pivot toward the San Francisco Bay, veer inland to the Nevada border, or ride the flatlands south toward Los Angeles. It's an important junction for any California driver -- and, in a sense, a symbol of California's climate choices. The state already has plans to widen Highway 99 to deal with increased traffic in the coming decades. But boosters of high-speed rail for the state say no amount of road expansion will be able to serve a larger population. Build the train, supporters say, and the state will cause far less greenhouse gas emissions than if Californians took all their trips by car and plane instead.