Extended bottlenecks, the fundamental relationship, and capacity drop on freeways

Coifman, Benjamin; Kim, Seoungbum

doi:10.1016/j.tra.2011.04.003

Cited by 26 publications

(28 citation statements)

References 24 publications

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“…. The right-hand side of the figure shows the qkFR, which is set to be triangular (see, e.g., [5,13]). However, the specific shape of the qkFR is not critical to the general findings of this paper.…”

Section: Homogeneous Vehicles Stationary Traffic Long Sampling Periodmentioning

confidence: 99%

Jam Occupancy and Other Lingering Problems with Empirical Fundamental Relationships

Coifman

2014

Transportation Research Record: Journal of the Transportation R

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This paper explores several commonly overlooked factors impacting empirical fundamental relationships that are commonly used to relate the traffic state parameters: speed, flow and concentration. Most of these factors are conceptually simple, but collectively they result in surprisingly large, non-linear distortions of the empirical traffic state measurements. In some cases the impacts are known but underappreciated, e.g., passenger car equivalents and measurement errors arising from sampling artifacts. In other cases the impacts have not been recognized in the literature, e.g., we find that jam occupancy should be about 80%. We also discuss often-overlooked impacts from an inhomogeneous vehicle fleet and non-stationary traffic, both of which can add considerable noise to empirical measurements of the traffic state. As a result of these distortions, on a freeway we find that over half of the physical distance along the queued regime of the fundamental relationship in the flow-density plane (and flow-occupancy plane) come from speeds below 10 mph. This fact inadvertently gives greater weight to the low-speed measurements because they are spread over a large physical region of the plane while the higher speed measurements are compressed into a narrow sliver. Unfortunately, as we illustrate, the low-speed samples are subject to the largest measurement errors, are the least likely to come from stationary conditions, and they often violate the assumptions used to measure the traffic state. In short, aggregated low-speed data from conventional vehicle detectors should be discounted or possibly discarded when constructing an empirical fundamental relationship.

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Section: Homogeneous Vehicles Stationary Traffic Long Sampling Periodmentioning

confidence: 99%

Jam Occupancy and Other Lingering Problems with Empirical Fundamental Relationships

Coifman

2014

Transportation Research Record: Journal of the Transportation R

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“…(17)- (20), impacts of different driver behaviors or car characteristics, e.g. (5), (7), (21), (22), lane changes and the global acceleration process that happens downstream of the merge, e.g. (23)- (25).…”

Section: Introductionmentioning

confidence: 99%

Capacity Drops at Merges: Analytical Expressions for Multilane Freeways

Leclercq

Marczak

Knoop

et al. 2016

Transportation Research Record: Journal of the Transportation R

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This paper deals with the derivation of analytical formulae to estimate the effective capacity at freeway merges in a multilane context. It extends two previous papers that are based on the same modeling framework but that are restricted to a single lane on the freeway (or to the analysis of the right lane only). The analytical expression for the one-lane capacity is recursively applied for all lanes. Lane-changing maneuvers (mandatory for the on-ramp vehicles and discretionary for others) are partitioned into two non-overlapping local merging areas. Discretionary lane-changes are transformed into a lane-changing flow using an appropriate analytical formula. This defines a system of equations whose unknowns are the capacity on all lanes and the inserting flow coming from the on-ramp. A sensitivity analysis shows that vehicle acceleration and the truck ratio are the most influential parameters for the total capacity. The analytical formulae are proven to match with numerical results from a traffic simulator that fully describes vehicle dynamics. Finally, they provide very good estimates when compared to experimental data for an active merge on the M6 freeway in UK.

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“…In the past decades, continuous effort has been devoted to the study of capacity of on-ramp merging section. Many researchers have tried to identify the causes of capacity drop at on-ramp merging section that seems to be linked to flow interference, which are created by vehicle lane-changing maneuvers [1][2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Capacity Estimation for On-Ramp Merging Section of Urban Expressway Based on Time Headway Loss

Xingjian

Shi

Cai

2014

Discrete Dynamics in Nature and Society

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This paper proposes a model for estimating capacity of on-ramp merging section of urban expressway based on dynamics and gap acceptance theory, considering lane-changing processes and time headway loss. Survey data were collected from on-ramp merging sections of shanghai urban expressway system and showed that capacity drop of on-ramp merging section is caused by drivers’ lane-changing which may lead to unsteady speed of vehicles and so prolonged time headway compared to the minimum time headway corresponding to the maximum capacity. Three parameters (optimal time headway, time headway loss, and interference quantity of lane-changing) are given and a methodology by accumulating time headway loss due to lane-changing is developed to estimate the capacity drop. Results’ comparisons between real data and microsimulation of on-ramp merging sections and sensitivity analysis show that the proposed model can produce reliable and accurate results. This study also reveals that ramp flow and the difference between the optimal speed and the lane-changing speed of fleet have a great impact on capacity drop. This study is beneficial to evaluate congestion levels, to understand complex traffic phenomena, and so to find efficient solutions.

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Extended bottlenecks, the fundamental relationship, and capacity drop on freeways

Cited by 26 publications

References 24 publications

Jam Occupancy and Other Lingering Problems with Empirical Fundamental Relationships

Jam Occupancy and Other Lingering Problems with Empirical Fundamental Relationships

Capacity Drops at Merges: Analytical Expressions for Multilane Freeways

Capacity Estimation for On-Ramp Merging Section of Urban Expressway Based on Time Headway Loss

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