Traffic Operations and Management

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...

Allocating City Space to Multiple Transportation Modes: A New Modeling Approach Consistent with the Physics of Transport

Gonzales, Eric J.
Geroliminis, Nikolas
Cassidy, Michael J.
Daganzo, Carlos F.
2008

A macroscopic modeling approach is proposed for allocating a city’s road space among competing transport modes. In this approach, a city or neighborhood street network is viewed as a reservoir with aggregated traffic. Taking the number of vehicles (accumulation) in a reservoir as input, we show how one can reliably predict system performance in terms of person and vehicle hours spent in the system and person and vehicle kilometers traveled. The approach is used here to unveil two important results: first, that restricting access to a city’s congested areas can improve mobility for all...

Effects of High Occupancy Vehicle Lanes on Freeway Congestion

Daganzo, Carlos F.
Cassidy, Michael J.
2008

Previous research on the effect of HOV (high occupancy vehicle) lanes on bottleneck flows is extended here to entire freeways using both theory and empirical evidence. The paper shows that if the flows of both high- and low-occupancy vehicles remain invariant before and after a freeway lane is converted to HOV use, then the freeway’s overall traffic density upstream of its bottlenecks is reduced – albeit less than expected – if the HOV lane is underutilized. As a result, HOV lanes can extend queues over longer distances. These expansions can be problematic if the queues’ expanded portions...

Spatiotemporal Effects of Segregating Different Vehicle Classes on Separate Lanes

Cassidy, Michael J.
Daganzo, Carlos F.
Jang, Kitae
Chung, Koohong
Lam, William H. K.
Wong, S.C.
Lo, Hong K.
2009

The paper explores some of the impacts of setting aside road lanes for the exclusive use of select vehicle classes. We examine first the case of lanes that are reserved for carpools, and then extend the analysis to bus-only lanes. In doing so, the paper makes three contributions. The first is methodological: it illustrates the importance of analyzing freeway data in full spatiotemporal detail. The second is physical: data reveal that carpool lanes are not as damaging as previously reported. In fact, these lanes are found to smooth traffic in adjacent lanes so much (by diminishing...

Multimodal Traffic at Isolated Signalized Intersections: New Management Strategies and a Framework for Analysis

Xuan, Yiguang
Gayah, Vikash V.
Daganzo, Carlos F.
Cassidy, Michael J.
2010

New ideas are explored for managing multimodal traffic on isolated approaches to signalized intersections. Strategies are proposed that both: segregate distinct modes along the approach, and more effectively resolve the disruptive capacity-reducing conflicts that arise between through-moving and turning traffic traveling in adjacent lanes. The various schemes for doing this are systematically enumerated, using as a building block the simple case of an intersection approach on which two movements are in conflict; and a framework is formulated for estimating the capacities that these...