Adaptive Planning for Transportation Corridors Threatened by Sea Level Rise

Abstract

This paper describes a generalizable planning and assessment process for transportation planning adaptive to sea level rise (SLR). State Route 37 (SR-37) is the California highway most vulnerable to temporary flooding and permanent inundation as a result of SLR. Like many other coastal highways in the United States, SR-37 is adjacent to protected coastal systems (e.g., beaches, tidal wetlands), meaning that any activity on the highway is subject to regulatory oversight. Both SR-37 and the surrounding marshes are vulnerable to the effects of SLR. Because of a combination of congestion and threats from SLR, planning for a new highway adaptive and resilient to SLR impacts was conducted in the context of stakeholder participation and Eco-Logical, a planning process developed by FHWA to better integrate transportation and environmental planning. To understand which stretches of SR-37 might be most vulnerable to SLR and to what degree, a model of potential inundation was developed with a recent, high-resolution elevation assessment conducted using lidar. This model projects potential inundation by comparing future daily and extreme tide levels with surrounding ground elevations. The vulnerability of each segment was scored according to its exposure to SLR effects, sensitivity to SLR, and adaptive capacity (ability of other roadways to absorb traffic). The risk to each segment from SLR was determined by estimating and aggregating impacts to costs of improvement, recovery time (from impacts), public safety impacts, economic impacts, impacts on transit routes, proximity to communities of concern, and impacts on recreational activities.