Traffic Operations and Management

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...

A Congestion Mechanism for Uphill Expressways, Part I: The Shoulder Lane "Release Valve"

Patire, Anthony D.
Cassidy, Michael J.
2010

A mechanism is unveiled by which congestion forms and persists near the base of an uphill expressway segment, causing significant reductions in output flow. The traffic condition in the expressway's shoulder lane is key to the mechanism. When shoulder-lane flow was low, drivers maneuvered around speed disturbances that periodically arose in the median lane. The shoulder lane accommodated high rates of vehicle migrations, thus acting as a "release valve" for the excess accumulation created by the speed disturbances. The release valve failed only when demand increased later in the rush. The...

On-Ramp Metering and Commuter Delay: A Before and After Study

Kim, Kwangho
Cassidy, Michael J.
2010

This report furnishes clear evidence that on-ramp metering can increase the output flow through a freeway, and by so doing diminish the total time that commuters collectively spend traveling on the freeway and its on-ramps. Empirical study was performed on a 6.3-mile stretch of northbound Interstate 5 in Sacramento. The stretch spans the interchanges of Pocket Road (to the south) to W street (See Figure 1). Traffic data, both from loop detectors and from videos, were collected during the morning rush periods over a period spanning several years. Data were initially collected in 2006 prior...

Deploying Underutilized Bus Lanes at Key Nodes in a Road Network

Guler, Ilgin
Cassidy, Michael
2010

The authors of this working paper explain that the operation of buses in mixed traffic flow can be impeded by congestion, leading to unreliable and slow service. Similarly, buses that stop frequently for passengers interfere with the flow of general traffic. Dedicated lanes provide a means for buses to bypass car queues, but in cases where bus flow is low, converting a general purpose lane to a bus-only lane will delay car traffic. The authors describe innovative schemes for deploying bus lanes to serve low bus demand intermittently. Strategies to deploy underutilized bus lanes will be...

Public Transportation Systems: Mini-Projects and Homework Exercises

Gonzales, Eric J.
Pilachowski, Josh
Gayah, Vikash V.
Cassidy, Michael
Daganzo, Carlos F.
2010

The Course Notes for a graduate-level course in Public Transportation include seven homework exercises and three mini-projects. Homework topics include optimization, point-to-point travel, congestion relief, designing a feeder bus system, demand-responsive transit, and bus pairings. The mini-projects involve bus rapid transit, designing a transit network, and bus and driver assignment.

Lane Changing Patterns of Bane and Benefit: Observations of an Uphill Expressway

Patire, Anthony D.
Cassidy, Michael J.
2011

A mechanism is unveiled by which congestion forms on a 3-lane, uphill expressway segment, and causes reductions in output flow. Vehicular lane-changing (LC) is key to the mechanism, particularly LC induced by speed disturbances (SDs) that periodically arise in the expressway’s median and center lanes. Early in the rush, when flow was relatively low in the shoulder lane, drivers readily migrated toward that lane to escape the oncoming SDs. The shoulder lane thus acted as a ‘release valve’ for the high vehicular accumulations created by the SDs, such that forced vehicular decelerations were...

Strategies for Mitigating Impacts of Near-Side Bus Stops on Cars

Gu, Weihua
Cassidy, Michael J.
Gayah, Vikash V.
Ouyang, Yanfeng
2012

"Near-side stops" are bus stops located a short distance upstream of a signalized intersection. A bus dwelling at a near-side stop can impede queued cars upstream as they discharge during their green time at the intersection. Added car delays and residual queues can result. All else equal, the closer the stop’s location to the intersection, the greater the potential damage to car traffic. Models for locating these near-side stops to achieve target levels of residual queueing among cars are formulated using kinematic wave theory. This same approach was also used to develop a strategy for...

A Capacity-Increasing Mechanism in Freeway Traffic

Kim, Kwangho
Cassidy, Michael J.
2012

A reason is unveiled for the time-varying pattern in discharge flow that is commonly observed at freeway bottlenecks. We hypothesize that four known effects in freeway traffic can interact upstream of a bottleneck in ways that trigger periodic bursts in its discharge flow. Repeated observations of a 3-km freeway stretch support the hypothesis. Controlled experiments show that the capacity-increasing mechanism can be favorably modulated by metering the site’s on-ramps in an unconventional manner. The unconventional strategy repeatedly produced higher average discharge flows and shorter on-...

Inhomogeneous Flow Patterns in Undersaturated Road Networks: Implications for Macroscopic Fundamental Diagram

Doig, Jean C.
Gayah, Vikash V.
Cassidy, Michael J.
2013

Travel conditions on a road network are described by a macroscopic fundamental diagram (MFD) only when traffic is homogeneously distributed over all of the network's links. Otherwise, a network's measured traffic states fall beneath its MFD, and network flow therefore falls below the maximum. The present study found that inhomogeneous link flowed in a network may emerge before the beginning of a peak period, even before persistent queues had formed. This finding is potentially problematic because it is known that inhomogeneities of this kind can persist in a network for long durations....

Mitigating Negative Impacts of Near-Side Bus Stops on Cars

Gu, Weihua
Cassidy, Michael J.
Gayah, Vikash V.
Ouyang, Yanfeng
2013

Bus stops are often placed short distances upstream of signalized intersections. Buses that dwell at one of these so-called near-side stops can impede queued cars upstream from discharging through the intersection during green times. Residual car queues can form at the intersection as a result. The smaller the distance between a stop and its intersection, the greater the problem can be. Models are formulated to address this problem using kinematic wave theory. The models can be used to determine where to place a near-side stop to achieve a target level of residual car queueing. In addition...