Observations at a Freeway Bottleneck

Using transformed curves of cumulative vehicle count and cumulative occupancy, a study was conducted of traffic upstream and downstream of a bottleneck on a freeway in Toronto, Canada, located more than a kilometer downstream of a busy on-ramp. After diagnosing its location and the times that it remained active each day, the study focused on the traffic patterns that arose in each travel lane. It was observed that prior to the bottleneck's activation, vehicle lane-changing trends created extraordinarily high flows in the median (i.e., left-most) lane and that these high flows were sustained for extended durations. When a queue eventually formed at the bottleneck, its discharge rates were considerably lower than those flows measured prior to queueing. Within each lane, the queue discharge rates remained nearly constant over the rush and the average rates varied only slightly across days. Finally, vehicles arriving at the bottleneck from the nearby upstream on-ramp entered the freeway at high rates, even after the bottleneck's queue propagated beyond this ramp.