Traffic Operations and Management

Maximizing Bus Discharge Flows from Multi-Berth Stops by Regulating Exit Maneuvers

Gu, Weihua
Cassidy, Michael J.
2013

Upon having loaded and unloaded their passengers, buses are often free to exit a multi-berth bus stop without delay. A bus need not wait to perform this exit maneuver, even if it requires circumventing one or more other buses that are still dwelling in the stop’s downstream berths. Yet, many jurisdictions impose restrictions on bus entry maneuvers into a stop to limit disruptions to cars and other buses. Buses are typically prohibited from entering a stop whenever this would require maneuvering around other buses still dwelling in upstream berths. An entering bus is instead required to...

Spatiotemporal Studies of Traffic Phenomenon on Freeways with Limited-access Special Lanes

Cassidy, Michael J.
Kim, Kwangho
2015

Most special-use freeway lanes in the US, whether reserved for carpools, toll-paying commuters or both, are physically separated from the adjacent regular-use lanes by some form of barrier. Vehicle movements in and out of a special lane of this type are permitted only at select access points along the route. The barrier at each select point might open for a distance of 400 m or so. Limiting access in this way is said to reduce the “turbulence” that might otherwise occur were the special lane not to have a buffer, such that vehicles could instead enter or exit that lane anywhere along its...

Models of Bus Queueing at Curbside Stops

Gu, Weihua
Cassidy, Michael J.
Li, Yuwei
2015

We consider curbside bus stops of the kind that serve multiple bus routes and that are isolated from the effects of traffic signals and other stops. A Markov chain embedded in the bus queueing process is used to develop steady-state queueing models of this stop type, as illustrated by two special cases. The models estimate the maximum number of buses that can arrive at and serve a stop and still satisfy a specified target of average bus delay. These models can be used to determine, for example, a stop’s suitable number of bus berths, given the bus demand and the specified delay target. The...

A Problem of Limited-Access Special Lanes. Part I: Spatiotemporal Studies of Real Freeway Traffic

Cassidy, Michael J.
Kim, Kwangho
Ni, Wei
Gu, Weihua
2015

Most special-use freeway lanes in the US, whether reserved for carpools, toll-paying commuters or both, are physically separated from the adjacent regular-use lanes by some form of barrier. Vehicle movements in and out of a special lane of this type are permitted only at select access points along the route. The barrier at each select point might open for a distance of 400m or so. Limiting access in this way is said to reduce the “turbulence” that might otherwise occur were the special lane not to have a barrier, such that vehicles could instead enter or exit that lane anywhere along its...

A Problem of Limited-Access Special Lanes. Part II: Exploring Remedies via Simulation

Ni, Wei
Cassidy, Michael J.
Kim, Kwangho
Gu, Weihua
2015

Spatiotemporal analyses of freeway sites in Part I have shown that special-lane access points are prone to become bottlenecks. These can degrade traffic flows, sometimes in all lanes. Part II explores select impacts of re-designing the means of entering and exiting a special lane, and of altering the policy governing its use. Parametric tests were conducted using a computer simulation model that was calibrated to one of the sites studied in Part I; one with a buffer-separated carpool lane. Though less reliable than what might have been observed via experiments in real settings, the...

A Low-Cost Alternative for Higher Capacities at Four-way Signalized Intersections

Kozey, Peter
Xuan, Yiguang
Cassidy, Michael J.
2016

Protecting left-turn movements on all four approaches to a signalized intersection conventionally requires a minimum of two extra phases per cycle. Losses in capacity often result. Various intersection designs have been proposed to combat those losses. Perhaps the best known of these designs is the continuous flow intersection. It features specially-configured approach lanes and mid-block pre-signals. These enable opposing left-turn and through-moving vehicles to proceed through the intersection free of conflicts, and without need for additional protected-turn phases. The present paper...

Cordon Control with Spatially-Varying Metering Rates: A Reinforcement Learning Approach

Ni, Wei
Cassidy, Michael J.
2019

The work explores how Reinforcement Learning can be used to re-time traffic signals around cordoned neighborhoods. An RL-based controller is developed by representing traffic states as graph-structured data and customizing corresponding neural network architectures to handle those data. The customizations enable the controller to: (i) model neighborhood-wide traffic based on directed-graph representations; (ii) use the representations to identify patterns in real-time traffic measurements; and (iii) capture those patterns to a spatial representation needed for selecting optimal cordon-...

City-Wide Traffic Control: Modeling Impacts of Cordon Queues

Ni, Wei
Cassidy, Michael
2019

Optimal cordon-metering rates are obtained using Macroscopic Fundamental Diagrams in combination with flow conservation laws. A model-predictive control algorithm is also used so that time-varying metering rates are generated based on their forecasted impacts. Our scalable algorithm can do this for an arbitrary number of cordoned neighborhoods within a city. Unlike its predecessors, the proposed model accounts for the time-varying constraining effects that cordon queues impose on a neighborhood’s circulating traffic, as those queues expand and recede over time. The model does so at every...

Region-Wide Congestion Prediction and Control Using Deep Learning

Mohanty, Sudatta
Pozdnukhov, Alexey
Cassidy, Michael
2020

Traffic congestion is forecast for neighborhoods within a region using a deep learning model. The model is based on Long Short-Term Memory (LSTM) neural network architecture. It forecasts a congestion score, defined as the ratio of the vehicle accumulation inside a neighborhood to its trip completion rate. Inputs include congestion scores measured at earlier times in neighborhoods within a region, and three other real-time measures of regional traffic. The ideas are tested using Newell’s simplified theory of kinematic waves. Simplified street networks are featured first. Initial tests...

How and When Cordon Metering Can Reduce Travel Times

Doig, Jean
Daganzo, Carlos F.
Cassidy, Michael J.
2024
The paper addresses two questions regarding cordon metering that have until now gone unanswered. The first of these pertains to how and where a metered cordon ought to be placed in a city to be of greatest benefit. A simple 3-step rule is proposed that can be readily applied in real settings, and that we call the cordon layout conjecture, or CLC. Its use is shown to minimize the overall travel time...