Variation in Freeway Lane Use Patterns with Volume,Time of Day,and Location

Lane flow data for five extended freeway segments in the San Diego, California, area were used to examine the effects of freeway and ramp volumes on lane flow distributions and to explore the extent to which these relationships vary by time and location. The proportion of the flow using particular lanes varies significantly with the freeway volume but not with the on-ramp volume. Relationships between freeway volume and the proportion of flow in particular lanes vary significantly by time of day, with flows in different lanes more nearly equal in midday periods than before the morning peak period or after the evening peak period. Such relationships are relatively similar for different days at the same location and different locations within the same extended freeway section but are quite dissimilar for different sections. As a general rule, the proportion of flow in the median lane increases with increasing volume and is greater than that for other lanes in congested flow and high-volume uncongested flow; however, in some cases it increases continuously with increasing volume, and in others it increases up to a point and then decreases. The major implications for behavioral theories of traffic flow are that lane use behavior varies with driver population characteristics and that in making lane use decisions, drivers are sensitive to both speed and vehicle spacing.