"Traffic. If you're a commuter, it's your daily torture. If you run a business, it represents hair-pulling risk and cost. The U.S. economy suffers a $160 billion annual hit in lost productivity from traffic jams, while drivers in some major cities spend up to two work weeks stuck bumper to bumper. Long and congested commutes even correlate with higher rates of divorce, stress, obesity and chronic pain. But all of this pales in comparison to the one, big, dirty secret of traffic: We know how to fix it."