Traffic Operations and Management

The Smoothing Effect of Carpool Lanes on Freeway Bottlenecks

Cassidy, Michael J.
Jang, Kitae
Daganzo, Carlos F.
2010

Real data show that reserving a lane for carpools on congested freeways induces a smoothing effect that is characterized by significantly higher bottleneck discharge flows (capacities) in adjacent lanes. The effect is reproducible across days and freeway sites: it was observed, without exception, in all cases tested. Predicted by an earlier theory, the effect arises because disruptive vehicle lane changing diminishes in the presence of a carpool lane. We therefore conjecture that smoothing can also be induced by other means that would reduce lane changing. The benefits can be large....

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.

On the Allocation of City Space to Multiple Transport Modes

Gonzales, Eric J.
Geroliminis, Nikolas
Cassidy, Michael J.
Daganzo, Carlos F.
2010

This paper analyzes urban multimodal transportation systems in an aggregated way. To describe the aggregate behavior of traffic in cities, use is made of an idea that is now receiving some attention: the macroscopic fundamental diagram (MFD). We demonstrate through simulation how the MFD can be used to monitor and control a real network, in this case a portion of San Francisco, using readily available input data. We then show how different modes interact on the same network and discuss how these interactions might be incorporated into an MFD for multimodal networks. The work unveils two...

Macroscopic Fundamental Diagrams for Freeway Networks: Theory and Observation

Cassidy, Michael J.
Jang, Kitae
Daganzo, Carlos F.
2011

Macroscopic fundamental diagrams (MFDs), which relate the total time spent to the total distance traveled, are explored for freeway networks. It is proposed that these macrolevel relations should be observed if the data come from periods when all lanes on all links throughout the network are in either the congested or the uncongested regime. The theory pertains to freeway networks of any size, even when they are inhomogeneously congested and the data are variable in time. Analysis of vehicle trajectories from two freeway stretches of modest physical length supports this theory. Study...

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...

Increasing the Capacity of Signalized Intersections with Separate Left Turn Phases

Xuan, Yiguang
Daganzo, Carlos F.
Cassidy, Michael J.
2011

A separate turn phase is often used on the approach leg to an intersections with heavy left turns. This wastes capacity on the approach because some of its lanes cannot discharge during its green phases. The paper shows that the problem can be eliminated by reorganizing traffic on all the lanes upstream of an intersection using a mid-block pre-signal. If drivers behave deterministically, the capacity that can be achieved is the same as if there were no left turns. However, if the reorganization is too drastic, it may be counterintuitive to drivers. This can be remedied by reorganizing...

Dual Influences on Vehicle Speeds in Special-Use Lanes and Policy Implications

Jang, Kitae
Cassidy, Michael J.
2011

Slow speeds in a special-use lane, such as a carpool (HOV) or bus lane, can be due to both high demand for that lane and slow speeds in the adjacent regular-use lane. These dual influences are confirmed from months of data collected from all freeway carpool facilities in the San Francisco Bay Area. Both influences hold for other types of special-use lanes, including bus lanes. New US regulation stipulating that most classes of low-emitting vehicles, or LEVs, be banned from slow-moving carpool lanes. While LEVs invariably constitute only about 1 percent of the freeway traffic demand in the...