OPTIMAL URBAN LAND USE UNDER MULTI-MODAL TRANSPORTATION

从全球环境问题的角度来看，交通领域的节能也是当务之急。在城市交通中，已经提出了几种节能的方法，如对汽车征收拥堵税，在市中心利用轻轨，以及发展电动汽车。其中一个经典的建议是所谓的“停车转乘”系统，我们使用汽车从住处到附近的火车站，然后转乘铁路到CBD，工作场所。通过这种方式，应该减少汽车的私人使用，从而大大改善市中心的拥堵和环境负外部性。在城市经济学的文献中，有一系列关于铁路竞争的相关问题(参见Kanemoto 1984等)，但它缺乏环境观点。虽然交通工程师对这种系统的重要性争论不休，但该系统的经济意义还没有得到足够的推导。在这项研究中，我们将开发一个简单的城市停车换乘系统模型。也就是说，假设一个单中心城市，几条铁路从一个CBD到郊区，家庭首先使用汽车从每户人家到最近的火车站，在那里换乘开往CBD的铁路，或者他们可以选择乘坐私家车直接到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。由于在区位或空间上存在差异的铁路公司之间的垄断竞争中，汽车直接通勤是一种“外部性商品”，我们遵循Salop(1979)的模型，通过引入扭结需求曲线，分析了横向差异化市场中外部性商品的作用，得到了反常的特征。

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.