More than 50% of congestion occurs in uninterrupted flow sections of sag or upgrade slope and tunnel entrance on intercity expressways in Japan. It is urgent and important to take costeffective soft measures to mitigate traffic congestion. Based on the result of several experiments by providing bottleneck location information with simple variable message sign, this study aims to evaluate the effect of the variable message sign on increase of bottleneck capacity. As a result, observed queue discharge flow rate is increased by 5-15%, which could recover 25% to nearly 90% of capacity drop after congestion depending upon bottleneck. A mechanism is described from the viewpoint of drivers' behavior. The increase of pre-queue breakdown flow rate could also be expected sometimes.
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