OPTIMAL URBAN LAND USE UNDER MULTI-MODAL TRANSPORTATION

从全球环境问题的角度来看，交通部门的节能也是当务之急。城市交通节能的途径主要有征收交通拥挤税、在城市中心区利用轻轨、发展电动汽车等。其中一个经典的建议是所谓的“停车换乘”系统，我们使用汽车从住宅到附近的火车站，然后转乘铁路到CBD和工作场所。通过这种方式，可以减少汽车的私人使用，从而大大改善市中心的交通拥挤和环境负外部性。在城市经济学的文献中，虽然有关于铁路竞争的相关问题的研究（见Kanemoto 1984等），但缺乏环境观点。虽然交通工程师们一直在讨论停车换乘系统的重要性，但对停车换乘系统的经济意义还没有得到充分的研究。也就是说，假设一个单中心的城市，多条铁路从一个单一的CBD到郊区的辐射状，家庭首先使用汽车从自己的房子到最近的火车站，他们在那里转乘开往CBD的铁路，或者他们可以选择乘坐私人汽车直接到CBD。因此，在这种模式下，既有铁路之间的竞争，也有铁路与汽车之间的竞争。由于在铁路公司之间的垄断竞争中，汽车直接通勤作为“外部商品”发挥作用，这些铁路公司在地理位置或空间上存在差异，因此我们遵循Salop（1979）的模型，分析了外部商品在水平差异市场中的作用，并由于引入了扭曲的需求曲线而获得了反常的特征。

From the viewpoint of global environmental issues, it is urgent to save energy in transport sector as well. There have been several ways proposed for saving energy in urban transportation, such as congestion tax on automobile, utilization of light rail in down towns, and development of battery cars. One of those classic proposals is so-called "park-and-ride" system that we use automobiles from housed to railway station nearby and transfer to railways to CBD, working places. By this way, the private use of automobiles should be reduced so that congestion as well as environmental negative externality in downtown would be improved much.In the literature of urban economics, there is a stream on related issues of railway competition (see Kanemoto 1984 among others), yet it lacked for the environmental viewpoint. While transportation engineers argued the importance of such system, economic implication of the system has not been derived enough.In this reserch, we will develop a simple model of park-and-ride system in urban setting. That is, suppose a monocentric city where several railways start from a single CBD to suburb area spoke-wise, and households use automobiles first from each own house to nearest railway station circumferentially where they transfer to railways bound for CBD, or they may choose to ride private cars to CBD directly. Hence, there are competitions between railways as well as between railway and automobiles in this model. Since direct commuting by automobiles works as "outside good" in monopolistic competition among railway companies those are differentiated in location or space, we follow the model by Salop (1979) that analyses the work of outside good in horizontally differentiated market and obtains perverse characteristics due to the introduction of kinked demand curve.