New Methods for Determining Capacity of Bottlenecks on Freeways

Accurate determination of capacity of bottlenecks is essential for proper traffic management in and around bottlenecks. Restrictions in roadway geometry or traffic composition, or implementation of new operational policies may create a chock-point on a freeway. Regardless of the cause of bottleneck, the effects are often congestion, queue, and increase in travel time. Bottlenecks may also create unsafe driving conditions and may increase the chance of rear-end collisions. This paper presents two new methodologies for finding bottleneck (i.e. work zone) capacity and operating speed: Four-Regime Models (FRM) and Updated Highway Capacity Manual (UHCM). The paper briefly discusses the factors affecting speed and capacity, and then compares the values estimated by the two methods for four different real-world work zone scenarios. The scenarios cover different speed limits, presence of flagger, and work activity levels. The results showed that FRM estimated values for speed and capacity represent the conditions more accurately than UHCM results because the FRM directly considers the presence of flagger and work activity, but UHCM does not.

Keywords:

freeway , bottleneck , work zone , capacity , four-regime speed flow , congestion , queue