Traffic Operations and Management

On-Ramp Metering Experiments to Increase Freeway Merge Capacity

Cassidy, Michael J.
Rudjanakanoknad, Jittichai
2005

Observations of two freeway/on-ramp merges unveil the mechanism that causes their capacities to diminish when queues form just upstream. Field experiments at one of the sites demonstrate that by responding to occupancies measured near the merge, ramp metering can reverse this mechanism, or postpone its occurrence, and thereby generate higher merge capacities. Detailed observations at the second site imply that higher merge capacities can also be achieved using traffic control schemes that regulate inflows to the merge from the freeway shoulder lane. Collectively, the findings point to...

Empirical Reassessment of Traffic Operations: Freeway Bottlenecks and the Case for HOV Lanes

Cassidy, Michael J.
Daganzo, Carlos F.
Jang, Kitae
Chung, Koohong
2006

An earlier empirical study of San Francisco Bay Area freeways concluded that HOV lanes unfavorably affect freeway traffic by creating congestion. That study attributed the observed congestion to HOV lanes and tentatively recommended their elimination over the full lengths of the freeways it examined; and even from all Bay Area freeways. It recognized, however, that its analysis is fragmentary and recommended further work to solidify its conclusions. This is logical since the study lacks a spatiotemporal analysis to pinpoint where and how congestion first forms (at bottlenecks).The present...

Impacts of Lane Changes at Merge Bottlenecks: A Theory and Strategies to Maximize Capacity

Laval, Jorge
Cassidy, Michael
Daganzo, Carlos
Schadschneider, Andreas
Pöschel, Thorsten
Kühne, Reinhart
Schreckenberg, Michael
Wolf, Dietrich E.
2007

Recent empirical observations at freeway merge bottlenecks have revealed (i) a drop in the bottleneck discharge rate when queues form upstream, (ii) an increase in lane-changing maneuvers simultaneous with this “capacity drop”, and (iii) a reversal of the drop when the ramp is metered.

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...

Freeway Traffic Oscillations and Vehicle Lane-Change Maneuvers

Ahn, Soyoung
Cassidy, Michael J.
2007

This work unveils the influence of vehicular lane-change maneuvers on oscillations in real freeway traffic. Measurements made upstream of bottlenecks reveal that oscillations formed in individual lanes when drivers squeezed their way in from neighboring lanes. Once oscillations had formed, moreover, lane changing caused the oscillations to at times grow in amplitude as they propagated upstream through queues. The findings how that on multi-lane freeways where lane changing abounds, these maneuvers seemingly exert greater influence on the formation and growth than do driver...

Impacts of Lane Changes at Merge Bottlenecks: A Theory and Strategies to Maximize Capacity

Laval, Jorge
Cassidy, Michael
Daganzo, Carlos
Schadschneider, Andreas
Pöschel, Thorsten
Kühne, Reinhart
Schreckenberg, Michael
Wolf, Dietrich E.
2007

Recent empirical observations at freeway merge bottlenecks have revealed (i) a drop in the bottleneck discharge rate when queues form upstream, (ii) an increase in lane-changing maneuvers simultaneous with this “capacity drop”, and (iii) a reversal of the drop when the ramp is metered.

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...

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...