USA: National map of communities with limited evacuation routes

Streetlight Data analyzed the approximately 30,000 towns in the U.S. with populations under 40,000 based on U.S. Census, scoring them using a ratio of the number of roadway "exits" from each town and the average "load" on the most-used exits, weighted by town population. Streetlight Data then selected a subset of approximately 800 communities that scored at least 3 times the average of all towns analyzed, which are shown on this map.