ABSTRACT
In recent years, traffic congestion in urban areas has become a major problem as the Japanese population becomes more and more concentrated in large cities. To alleviate traffic congestion, expressways have been constructed in the large cities. The construction of the expressway system in the Tokyo metropolitan area began in the 1960s, but the construction of circular expressways lags far behind the construction of radial expressways, as shown in Fig. 1. When expressway construction started in the 1960s, elevated expressways over the public right-of-way were built to expedite the construction schedule and to minimize the construction cost. However, due to environmental problems and overcrowded ground-level space, plans were made to construct the first underground expressway in Tokyo.
