Abstract
One or two years after the development of the transportation infrastructure, it will be a topic in the media whether the initial demand forecast was correct or not. However, because the effects of infrastructure improvement are realized through social change, it takes a very long time for appropriate assessment to be possible. In the series of Comprehensive National Development Plans, Shikoku was considered as one of the development target areas, and Honshu-Shikoku Bridges were developed for the purpose of overcoming the geographical obstacle of the Seto Inland Sea. More than 30 years have passed since Seto Ohashi Bridge was opened in 1988, also more than 20 years have passed since the opening of other routes, and it is now time to be able to perform an appropriate ex-post evaluation. Therefore, in this study, it was analyzed the long-term trends of population and gross prefecture product in four areas of San-in, San-yo, Seto-inside of Shikoku, and the Pacific side of Shikoku. After removing national trends from annual data of population and gross prefecture product, and removing the influence of regional population size and economic size, the essential ups and downs of the indicator were clarified. As a result, it was found that the population decline tendency of the Shikoku region had been relieved after route decision of Honshu-Shikoku Bridges. Furthermore, it was found that the population decline tended to be smaller than the Chugoku region after the bridges open. After the opening of the Seto Ohashi Bridge, the trend of gross prefecture product in Shikoku has got out of the long-term declining trend. The trend of gross prefecture product in Shikoku has shown the same or favorable tendency compared with the trend of the whole country. However, the gross prefecture product in Shikoku has been restricted by the nationwide stagnation since around 1992. This may be one of the causes of the continuous population diminishment in Shikoku.
