What causes those 'unexplainable' traffic jams?

CHICAGO (NEXSTAR) - Traffic jams are nearly unavoidable on highways and interstates. Sometimes it’s easy to explain — crashes, construction, and sudden influxes of cars, for example. Americans are spending more time stuck in traffic than in recent years. Data and analytics firm INRIX recently released its Global Traffic Scorecard, showing plenty of U.S. cities are among the most congested. Nationally, the study found U.S. drivers “lost” an average of 51 hours si