Traffic Theory

Driver Turn-Taking Behavior in Congested Freeway Merges

Cassidy, Michael J.
Ahn, Soyoung
2005

Data from four merge locations in northern California and Toronto, Ontario, Canada, unveil a notable feature of driver turn taking. It was observed that queued vehicles from the on-ramp and freeway traffic streams entered a congested merge in some (nearly) fixed ratio that was independent of the merge outflow. Drivers in competing traffic streams thus entered the merge by adopting some definite turn-taking behavior, and this behavior was not influenced by the severity of the exogenous flow restriction from downstream. The findings validate part of an existing theory of merging traffic and...

Driver Turn-Taking Behavior in Congested Freeway Merges

Cassidy, Michael J.
Ahn, Soyoung
2005

Data from four merge locations in northern California and Toronto, Ontario, Canada, unveil a notable feature of driver turn taking. It was observed that queued vehicles from the on-ramp and freeway traffic streams entered a congested merge in some (nearly) fixed ratio that was independent of the merge outflow. Drivers in competing traffic streams thus entered the merge by adopting some definite turn-taking behavior, and this behavior was not influenced by the severity of the exogenous flow restriction from downstream. The findings validate part of an existing theory of merging traffic and...

Relation Between Traffic Density and Capacity Drop at Three Freeway Bottlenecks

Chung, Koohong
Rudjanakanoknad, Jittichai
Cassidy, Michael J.
2007

Three freeway bottlenecks, each with a distinct geometry, are shown to share a relation between vehicle density and losses in discharge flow. Each bottleneck suffered reductions in discharge once queues formed just upstream. This so-called “capacity drop” was related to the density measured over some extended-length freeway segment near each bottleneck. Pronounced increase in this density always preceded a capacity drop. For each bottleneck, the densities that coincided with capacity drops were reproducible. When normalized by a bottleneck’s number of travel lanes and averaged across...

Deploying Lanes for High Occupancy Vehicles in Urban Areas

Cassidy, Michael J.
Daganzo, Carlos F.
2007

Simulations and field experiments in previous works suggest that a freeway’s general purpose lanes (those not dedicated to high occupancy vehicles) discharge vehicles from bottlenecks at an equal or higher average rate when one of the lanes is devoted to high occupancy vehicles than when it is not. This result was used in these previous works to develop formulae for the total discharge rate of bottlenecks, with and without dedicated lanes, as a function of the percentage of high occupancy vehicles in the traffic stream.This present paper extends these ideas by examining the effect of...

Effects of Merging and Diverging on Freeway Traffic Oscillations

Ahn, Soyoung
Cassidy, Michael J.
Laval, Jorge A.
2007

This paper proposes a theory for explaining the growth of oscillations as they propagate through congested merges and diverges. The idea is that merging or diverging flows change in response to freeway oscillations, and these changes have an effect of dampening (merging) or amplifying (diverging) oscillations. In this theory, a reduction or an increase in amplitude is quantified based on a single parameter (a fraction of entering flow for the merging effect and a fraction of exiting flow for the diverging effect). The effect of merging has been verified at multiple freeway merges where...

Deploying Lanes for High Occupancy Vehicles in Urban Areas

Cassidy, Michael J.
Daganzo, Carlos F.
2007

Simulations and field experiments in previous works suggest that a freeway’s general purpose lanes (those not dedicated to high occupancy vehicles) discharge vehicles from bottlenecks at an equal or higher average rate when one of the lanes is devoted to high occupancy vehicles than when it is not. This result was used in these previous works to develop formulae for the total discharge rate of bottlenecks, with and without dedicated lanes, as a function of the percentage of high occupancy vehicles in the traffic stream.This present paper extends these ideas by examining the effect of...

Effects of Merging and Diverging on Freeway Traffic Oscillations

Ahn, Soyoung
Cassidy, Michael J.
Laval, Jorge A.
2007

This paper proposes a theory for explaining the growth of oscillations as they propagate through congested merges and diverges. The idea is that merging or diverging flows change in response to freeway oscillations, and these changes have an effect of dampening (merging) or amplifying (diverging) oscillations. In this theory, a reduction or an increase in amplitude is quantified based on a single parameter (a fraction of entering flow for the merging effect and a fraction of exiting flow for the diverging effect). The effect of merging has been verified at multiple freeway merges...

An Empirical and Theoretical Study of Freeway Weave Bottlenecks

Lee, Joon
Cassidy, Michael J.
2008

Though there have been numerous studies of freeway weaving sections (i.e., segments in which an on-ramp is followed by an off-ramp), there remains a significant lack of empirical and theoretical understanding of the traffic behavior that causes weaving sections to become bottlenecks with varying discharge flows. The present research entails empirical analysis and theoretical modeling of what triggered the bottleneck activations and discharge flow changes in two freeway weaving sections. Both sites were recurrent bottlenecks during the rush, and investigations revealed that changes in the...

Effects of Merging and Diverging on Freeway Traffic Oscillations: Theory and Observation

Ahn, Soyoung
Laval, Jorge
Cassidy, Michael J.
2010

Continuum theory is used to explain why stop-and-go oscillations in congested freeway traffic change their amplitudes when they encounter the vehicular merging and diverging maneuvers that take place near ramps. The theory describes how oscillations diminish in amplitude when they propagate past a queued (and unmetered) on-ramp and how they grow when they propagate past an off-ramp. The premise is that merging (diverging) flows change in response to freeway oscillations and that these changes in flow dampen (amplify) oscillations. The theory's descriptions are simple and rational; all its...

Effects of Merging and Diverging on Freeway Traffic Oscillations: Theory and Observation

Ahn, Soyoung
Laval, Jorge
Cassidy, Michael J.
2010

Continuum theory is used to explain why stop-and-go oscillations in congested freeway traffic change their amplitudes when they encounter the vehicular merging and diverging maneuvers that take place near ramps. The theory describes how oscillations diminish in amplitude when they propagate past a queued (and unmetered) on-ramp and how they grow when they propagate past an off-ramp. The premise is that merging (diverging) flows change in response to freeway oscillations and that these changes in flow dampen (amplify) oscillations. The theory's descriptions are simple and rational; all its...