This paper discusses motorway traffic jams and their possible relief, and presents some results of the study of congestion in the Kobotoke Tunnel on the Chuo Motorway in Japan. Tunnels and vertical alignment sags can be one cause of decreased running speeds, which can lead to congestion or even to bottlenecks. The process for a formation of a bottleneck, under such circumstances, is described. The following traffic characteristics are found when traffic phenomena are investigated in detail at congestion points: (1) unbalanced lane use; (2) insufficient acceleration; (3) shock waves; (4) discharge flow rate; (5) low rate of acceleration; and (6) free flow in relation to congested flow. The objectives of countermeasures on the eastbound lane of the Kobotoke Tunnel are to: (1) reduce sudden changes of road environment at the entrance; and (2) correct traffic flow, by providing an artificial bottleneck on an open section in front of the tunnel entrance. Another possible measure is to widen the motorway from four to six lanes. In general, countermeasures aim to raise the maximum volume before congestion and the discharge flow rate after congestion. Their approaches include: (1) platoon prevention; and (2) improved discharge flow rate.
Abstract