ABSTRACT
Today, one encounters a lot of traffic congestion and hears of people injured or killed by traffic accidents. Moreover, there has been no remarkable improvement in air pollution due to exhaust gases from vehicles inspite of the stringent regulation for vehicles. It is natural that frequent traffic congestion results in lower mean vehicle speed. Figure 22.1 shows an example of mean averaged vehicle speed in Japan. Vehicle speed in urban area like Tokyo and Osaka is very dose to that of a bicycle. On the contrary, vehicle speed in countryside is faster than urban area. Therefore, average vehicle speed of the whole of Japan shows a little bit higher value, as shown in Fig. 22.1.
