There are about 1 billion cars on the world’s roads today. By mid-century, forecasts have that number climbing to 4 billion. Meanwhile, Congress is mired in a debate over whether to pass a new highway bill. Senator Barbara Boxer, a chief negotiator of the pending bill, lamented recently that she was “embarrassed for the people of this country” that this measure had not been enacted. After all, she said, passing highway bills used to be as popular and as important as “motherhood and apple pie.”