Last year, the average American driver wasted 38 hours sitting in traffic. While the occasional traffic jam inconveniences most drivers, some unlucky people live in the nation’s most congested cities. To determine the 10 cities with the worst traffic, 24/7 Wall St. reviewed figures published by INRIX, a traffic information and services group. The INRIX scorecard assigns an index score for the 100 largest metropolitan statistical areas, and individual road segments within those areas. Scores are functions of the percentage difference between road segments’ uncongested (or “free flow”) travel time and the calculated travel time on the roads during peak hours. 24/7 Wall St. also reviewed population density from the 2010 Census, as well as travel time and commuting methods for each metro area from the Census Bureau’s 2011 American Community Survey. All data used were the most recent available. These are the 10 cities with the worst traffic.