Abstract:
This paper briefly reports the results of analyses on traffic flow data, which were recorded every five minutes by vehicle detectors for approximately one year at bottleneck sections (mainly sags and tunnel entrances) on suburban expressways in Japan. The analyses include the estimation of traffic volume just before the occurrence of congestion which can be considered close to the possible capacity of the bottleneck; and the factor analysis on the relationship between traffic volume and the number of lanes, the width of left side shoulder, the longitudinal gradient, the percentage of heavy vehicles, and the day of the week. The results of the factor analysis show that capacity per lane increases more than proportionally to the increment of the number of lanes; that the effects of the width of left side shoulder and the percentage of heavy vehicles are not prominent; and that traffic volume just before congestion tends to vary depending on the day of the week. The above results are found by the analyses which were carried out based on these conditions: that there are a lot of tunnels and sags in Japan due to its topographical features; that the maximum number of lanes of expressways is three for each direction; that traffic congestion more frequently occurs in Japan compared with other countries. These findings are expected to give useful suggestions also for studies in foreign countries.
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