Traffic operation on two-lane rural highways is unique; no lane change is permitted, and overtaking and passing are possible only inthe opposing lane of the oncoming traffic. Traffic flow and capacity characteristics on two-lane highways were investigated. Several models were developed for the relationships between flow parameters. The relationships varied from one road to another and were dependent on the characteristics of each site. Thus, the hourly capacity volume is not a clear, single value. It primarily depends on the geometric and traffic characteristics of the highway section and on the timeinterval for which the flow data are collected. The two-way hourly capacity value was found to be about 2, 650 passenger cars per hour in both directions. This value was close to the general (extended section) capacity given in the highway capacity manual (hcm) for conditions similar to those in this study. The speeds at which capacity occurs, on the other hand, were lower than the hcm values: about 40 km/hr versus about 70 km/hr. Further research on the proper time interval for an analysis of highway capacity and on flow regimes and capacity values for various geometric, terrain, and traffic characteristics is suggested. This paper appears in transportation research record no. 1320, Freeway operations, highway capacity, and traffic flow 1991.
Abstract