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.
In 2012 when the superstorm Sandy hit New York, it caused a massive 14-foot storm surge and flooded some subway stations. This transportation service was shut down for days. The effect was much more significant because NYC is home to the most extensive public transportation system in the U.S. The hurricane Sandy provided analog to SLR, and the coastal zone will be increasingly at risk to episodic flood events superimposed on a more gradual rise in mean sea level (Gornitz, Couch, Hartig, & Change, 2001). The analysis by Climate Central Research(Research, 2016) aligns closely with the projection made by the NYC Panel on Climate Change projects the local sea level to rise from 0.6 – 1.8 feet by 2050, and 1.9 – 6.3 feet by 2100, using sea level in 2012 as the baseline.
Another non-motorized transportation mode such as bicycle lanes and pedestrian walkway are also prone to the effects of SLR and hence result in a decrease of accessibility/mobility in some low-lying parts (Barry, 2016; Upton, 2014). The impacts have been route closure, detour, or and completely impassable (Barry, 2016; Upton, 2014). In the case of Jacksonville, Florida, the nuisance flooding has occurred a few times a year, for instance, during a spring full moon tides (Barry, 2016). The Intracoastal residents have experienced waterfront in front of their houses, causing not only damage to their home and property but also disruption in daily activities (Barry, 2016). The high water level has made it difficult to move around, for instance from their house to the mailbox, and limit access to parks, and other locations (Barry, 2016). Some residents have forced out their completely flooded neighborhood (Barry, 2016). The flooding has had not only physical impact but also emotional because the residents expressed frustration for not able to be mobile (Barry, 2016). Besides Jacksonville, the Climate Central Research indicated population living in other low lying areas such as Sacramento, California, Virginia Beach, Virginia, Miami, and New Orleans are coastal and river cities most threatened in the U.S (Barry, 2016)
Since the beginning of this century, the Center for Climate Change and Environmental Forecasting at U.S. Department of Transportation began to pay attention to the issue of climate change and transportation. In 2002, it held the first workshop with the intent to explore the potential impacts of climate change on transportation and to delineate the research necessary to better understand these implications. Since then, many studies have been conducted to evaluate the impacts of climate change, particularly sea level rise, on transportation infrastructures (Burkett, 2002; Jacob, Gornitz, & Rosenzweig, 2007; Peterson, McGuirk, Houston, Horvitz, & Wehner, 2008; Savonis et al., 2008; Suarez et al., 2005; Titus, 2002). These studies addressed many relevant issues, ranging from sea level rise prediction to the identification of vulnerable transportation facilities and the associated economic costs, providing valuable information for sea level rise adaptation in coastal areas. However, most of these early studies focus on large scale qualitative analysis (Burkett, 2002; Savonis et al., 2008; Schmidt & Meyer, 2009; Titus, 2002); which is not specific or accurate enough to support local adaptation. Later some localized, quantitative studies have been developed. For instance, Bloetscher, Romah, Berry, Hammer, and Cahill (2012)identified vulnerable Florida’s state transportation infrastructure in Dania Beach and Punta Gorda under local sea level rise scenarios projected with Army Corps of Engineers’ scenario-based methodology, using Florida Department of Transportation (FDOT) information system, satellite imagery, local roadway and hydrologic data. Yet many studies only considers physical exposure rather than system impacts (Bloetscher et al., 2012; Walker, Figliozzi, Haire, & MacArthur, 2011; Wu et al., 2013). To overcome these limitations, some researchers used transportation model to estimate the system impacts (Han, Zegras, Rocco, Dowd, & Murga, 2017; Q. C. Lu & Z. R. Peng, 2011; Lu, Peng, & Du, 2012; Suarez et al., 2005). For example, Q. C. Lu and Z. R. Peng (2011)assess Miami’s transportation network’s vulnerability to projected 2060 sea level rise scenarios using accessibility based index.