The research involved 30,000 towns in the U.S. with populations under 40,000. These communities were scored 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. Eight hundred communities were selected because they scored at least three times the average risk of all the towns analyzed. These communities are seen on StreetLight's map.
Researchers developed an index based on the total number of routes out of town, the percentage of people who take certain routes on a typical day, and the total population. The data from this study can help towns consider the reality of evacuation plans in terms of road maintenance and availability when combined with human behavior.
There may be more than one route out of town, but many people will choose a certain route due to ease of use or habit. This is important information for emergency managers when they order an evacuation. It might prompt an earlier evacuation or calls to use a different route.
States with the most evacuation-challenged communities are:
Each of these states faces reoccurring threats from major natural disasters, such as hurricanes and large wildfires. Emergency Management Magazine has a list of the top 20 communities with the most constrained evacuation routes.