Stability of Freeway Bottleneck Flow Phenomena

Abstract

Data for 44 days from five extended freeway sections around bottlenecks in the San Diego, California, area were analyzed to determine the stability of the point of initial flow breakdown and the feasibility of using similar data for more extensive research into the stability of bottleneck flow phenomena. The ultimate goal of such research is to shed light on the nature of transitions from uncongested to congested flow. Analysis of speed drop sequences suggests that there is rarely a single bottleneck location within critical freeway sections. This in turn suggests that many bottlenecks should be thought of as extended sections rather than points or isolated segments. This suggests an understanding of flow transitions intermediate between the conventional view that flow breaks down consistently at a few locations and the view that flow breakdown is spontaneous and that congested flow is self-organized. Data similar to those used in this study are adequate, but not ideal, for further investigation of the stability of bottleneck flow phenomena. Specific limitations relate to the locations of detector stations and the presence of chronic data errors. This approach to the study of bottlenecks can be improved by combining direct observation with analysis of loop detector data and by using cumulative flow counts to estimate changes in the numbers of vehicles stored in freeway segments.

Investigation of the Relationship Between Upstream and on-Ramp Flows at Downstream Capacity Level on Istanbul Freeway Merges

“…If the speed dropped at further downstream RTMS before the downstream merge RTMS, this case is defined as the indicator of queue spillback. The capacity flow at downstream, formed by the upstream and on-ramp flows are distinguished by speed time series and re-scaled cumulative flow curves as previously mentioned in quite a few studies [18][19][20][21]. Core point of the analysis is to determine formation of capacity flow at downstream by on-ramp and upstream flows of a merge.…”

Counteracting traffic congestion using intelligent driver feedback

“…Flow breakdown occurs after a capacity threshold has been exceeded and can occur anywhere along sections of highway where the influences of fixed bottlenecks and traffic stream dynamics combine to precipitate capacity changes (Öǧüt and Banks, 2005). Capacity changes occur when traffic flow increases beyond road capacity or road capacity decreases below traffic flow.…”

“…); increases in traffic flow beyond capacity; or sometimes from transient disturbances, such as individual driver behavior, that the system is unable to absorb. When the capacity changes cross a non-deterministic threshold, congestion will result (Öǧüt and Banks, 2005).…”

“…A traffic shockwave is defined as the point of transition from one state of traffic flow to another (Öǧüt and Banks, 2005). A vehicle on an urban highway may travel at the speed limit in uncongested conditions (free flow), having little interaction with surrounding vehicles (in particular, the vehicle directly ahead), until the vehicle catches up to a slower vehicle.…”