Stationary Models of Unqueued Freeway Traffic and Some Effects of Freeway Geometry

Occupancies and flows were jointly sampled from numerous freeway segments in nearly stationary, unqueued traffic. The data from one segment were typically averaged across all lanes there and plotted. Each plot was compared with one sampled at a neighboring freeway segment, with the two segments differing only in their number of travel lanes. Such comparisons were repeated for a total of five pairs of segments on five freeways in and near Toronto, Canada and in California. All occupancy-flow relations were piece-wise linear in form for average flows up to about 2,000 vehicles per hour per lane. Only when traffic became moderately dense did average vehicle speeds diminish with increasing occupancies. The occupancy above which these speed diminutions occurred was the same for both segments in a pair. Notable, however, the average vehicle speed corresponding to a given occupancy was always higher on the segment with the larger number of lanes. The driver psychology that can explain some of these findings is discussed. Findings are also contrasted with information currently provided in traffic handbooks.