Evaluating Transportation Alternatives for Hattras Island, North Carolina Outer Banks

Abstract

The North Carolina coast includes a dynamic chain of barrier islands known as the Outer Banks. Transportation management on these islands has been the subject of debate over the past two decades because of the high cost of maintaining highway NC 12. The road is subject to frequent sand overwash and storm damage that causes interruptions in services and access and the bridge over a major inlet needs replacement. Interest groups disagree about the best solution, with some most concerned about environmental damage, some about economic impacts of service disruption, and some about emergency evacuation. We interviewed nine stakeholders from federal, state, and local government, citizen action groups, and environmental non-governmental organizations, asking them questions about their preferences pertaining to transportation in general and specific alternative transportation methods for the Outer Banks. The alternatives we researched were: (1) replacing the imperiled bridge with a new bridge across the same inlet (Short Bridge Plus), which would not alleviate the road maintenance difficulties on the islands; (2) building a long bridge through the sound behind the chain of barrier islands bypassing the troublesome road sections (Long Bridge) at very high initial cost; and (3) using ferries to provide transportation to the barrier islands (Ferry System), requiring extensive dredging of coastal habitat and high operational costs. Using data from archived reports and from our interviews, we compared these alternatives in terms of (1) access disruption from storm impacts (in days), (2) short-term cost (dollars), (3) long-term cost (dollars), and (4) environmental impacts (acres of habitat disturbed). We then interviewed three key stakeholders from state government, an environmental organization, and local government to determine how important each of the four factors was to each respondent in choosing a transportation alternative. By combining our evaluations of each alternative with the stakeholders’ judgments of importance, we found that the state representative chose the Short Bridge Plus, the environmental organization representative chose the Long Bridge, and the local government representative chose the Ferry System. Because some of these calculated results contradicted what these three respondents told us they preferred, we examined the sensitivity of our calculated results to changes in short and long-term cost estimates, acres disturbed and relative importance of the four factors. A consistent result of our sensitivity analyses was that stakeholders would often switch their preferred alternative to the Long Bridge. Therefore, we believe the Long Bridge might be a point of compromise; however, the massive funding required to build this alternative diminishes the likelihood it will be implemented.