Traffic Capacity of Alps Car Tunnels

Macroscopic traffic flow models play an important role in the planning, design, and operation of transportation facilities (Easa, 1980). In the last decades, the importance of highways as transportation facilities has been increased. However, there is lack of research about the performance of traffic flow in tunnels. Furthermore, building and operating costs of tunnel segments are much expensive than free highway segments. Therefore, reliable realization of traffic performance in tunnels is of great importance for economical planning of tunnels. Moreover, speed-flow relationship has more gradual slope with constant speed for higher levels of flow (Singh, 1999). In the light of recent research dealing with speed-flow models, this research aims at: (a) Investigation of speed-flow relationship in two-lane two-way Austrian tunnels during normal operating conditions; (b) Investigation of the effects of heavy traffic on the rate of speed reduction with the increase of traffic volume in tunnels and reviewing the passenger car equivalent factors that are used to convert traffic volume to passenger car units; (c) conducting of a speed-density relationship; and (d) estimation of lane capacity by transforming speed-density model to speed-flow relationship.