In the United States, roughly 40 percent of the population lives in relatively high-population-density coastal areas, where sea level plays a role in flooding, shoreline erosion, and hazards from storms (NOAA, 2018). Sea level rise and more frequent extreme events are expected to critically affect transportation (Becken, 2005). According to the U.S. Global Change Research program, approximately 60,000 miles of coastal roads in the United States are already exposed to flooding from coastal storms and high waves.

At the national scale, coastal states have endured more severe impact of flooding hazards on transportation compared to inland states. In another word, coastal flooding has more severe impacts on people’s travel than other types of flooding.