Observation of Congested Two-lane Traffic Caused by a Tunnel

We observe the congested traffic flow in Tomei Expressway, a Japanese expressway linking Tokyo with Nagoya. Congestion occurs at the upper stream of a traffic blockade, Nihonzaka tunnel, in contrast to preceding observations at the upper stream of an on-ramp. The flow on the fast lane is congested more severely than on the slow lane. The flow on the fast lane, however, almost always exceeds the one on the slow lane. The observed congested flow is stable and the average velocity on both lanes strongly correlated.