Basic Report

The impact of sea-crossing bridge on island residents is not limited to improved mobility. Sea-crossing bridge is expected to have a variety of impacts on island resident, including providing unrestricted traffic, changing land use and industry, and increasing property values. However, in assessing the economic value of sea-crossing bridges, the focus has been primarily on the impact on residents’ mobility, while relatively little attention has been paid to other expected effects. In this context, we investigated change in socioeconomic status, traffic attributes, and infrastructure in island areas due to the construction of sea-crossing bridges. We also conducted a survey to determine whether island residents were actually aware of these changes. The results of this study can be used as evidence to identify the true benefits of sea-crossing bridge projects and to develop related methodologies.
   We found that the sea-crossing bridges generated changes in various areas such as population, and industry, and that these changes are heterogeneous depending on the characteristics of each island. The construction of sea-crossing bridges has facilitated population mobility on the islands, but in some areas, the rapid increase in older population has accelerated aging. In terms of industry and land use, service and accommodation sectors, including restaurants, retail, and whole sales, mainly linked to the tourism industry, have grown noticeably. The development of the tourism and increased mobility have led to increase in income from the fishing and service industries. In terms of transportation, not only did the frequency of travel increase, but the travel time have also become more varied, showing that both mobility and traffic autonomy of island residents have been improved through sea-crossing bridges. A similar pattern was found in the survey. In particular, transportation inconveniences due to lack of traffic autonomy were noticeable. Despite the consensus among the island residents on the need for sea-crossing bridges, their willingness to pay for the bridge’s construction of was low.
   The results of this study imply that there are additional factors to consider when conducting feasibility studies for ocean-crossing bridge projects. In particular, it is necessary to investigate the effects of increasing income and property value in island areas due to sea-crossing bridges, and to consider the effects of improving traffic autonomy. Additionally, an in-depth review of the methodology for induced demand is necessary. A commonly used models assume that 50% of existing traffic is induced by demand. Because our results showed regional differences, induced demand model that takes regional differences into account is needed. It seems clear that sea-crossing bridges improve the mobility and traffic autonomy of island residents. However, it is still unclear whether these benefits are provided equally to all residents, or whether certain group of resident benefits from the bridge. Further research is required to examine this issue. One of the limitations of this study is that it was unable to consider long-term changes due to limitations in data collection. Examining these effects, however, should be investigated when relevant data are available.