Traffic Theory

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....

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...

Effects of Segregating Buses and Cars in a Congested, Non–Steady-State Street Network

Saade, Nathalie
Cassidy, Michael J.
Gu, Weihua
2015

Much of the literature on exclusive bus lanes pertains to how these lanes might induce shifts in mode choice by prioritizing bus travel, sometimes at the expense of degrading travel by car; for example, see Basso et al. (1). A separate line of research theorized that the conversion of regular-use lanes to bus-only lanes can, in certain circumstances, improve travel for cars as well as buses, even in the absence of modal shifts (2). By removing buses from queues and putting them in their own, faster-moving lanes, target service frequencies can be maintained with fewer buses; thus, fewer bus...

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...

Traffic Signal Plans to Decongest Street Grids

Sadek, Bassel
Doig Godier, Jean
Cassidy, Michael J.
Daganzo, Carlos F.
2022

Two new synchronization strategies are developed for signalized grids of two-directional streets. Both strategies are found to reduce congestion significantly more than do other approaches. One of the strategies is static and the other adaptive. Both use a common timing pattern for all signals on the grid but use a different offset for each. The static strategy serves the morning rush by providing perfect forward progression on all streets in the directions that point toward a reference intersection, one that is located near the center of gravity of all workplaces. For the evening rush,...

Traffic Signal Plans to Decongest Street Grids - Policy Brief

Cassidy, Michael J.
Daganzo, Carlos F.
Sadek, Bassel
Doig, Jean
University of California Berkeley. Department of Civil and Environmental Engineering
2022

The strategy retains excellent synchronization on these paths when adapting to residual queues. The synchronization is altered in these cases simply by replacing vehicle trip times with the trip times of backward waves that propagate through queues, as per kinematic wave theory. This has the desirable effect of preventing favored movements from being impeded by queues. (Green phases are initiated for a favored movement only after queues immediately downstream begin moving forward.) The strategy toggles between these forward and backward synchronization modes in zones that are subject to...

Traffic Signal Plans to Decongest Street Grids

Sadek, Bassel
Doig Godier, Jean
Cassidy, Michael J.
Daganzo, Carlos F.
2022

Two new synchronization strategies are developed for signalized grids of two-directional streets. Both strategies are found to reduce congestion significantly more than do other approaches. One of the strategies is static and the other adaptive. Both use a common timing pattern for all signals on the grid but use a different offset for each. The static strategy serves the morning rush by providing perfect forward progression on all streets in the directions that point toward a reference intersection, one that is located near the center of gravity of all workplaces. For the evening rush,...

Placement and Management of Bus Bypass Segments in Dense, Congested Cities

Bronicki, Nadav
Doig, Jean C.
Cassidy, Michael J.
University of California Berkeley. Department of Civil and Environmental Engineering
2023

In this research, simulation is used to explore how a bus bypass segment, also called a queue jump, affects traffic on a signalized arterial. Residual queues form at the site’s critical bottleneck and expand to street links upstream. A bypass, when designed to serve a bus stop as per AASHTO guidelines, is shown to reduce bus delays—if the stop resides on a congested link that is upstream of the one feeding traffic to the critical bottleneck. In contrast, using a bypass for a bus stop located immediately upstream of the critical bottleneck starves that bottleneck of flow. The damage thus...

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...

An Analysis of HOT Lanes in North Carolina

Benjamin, JM
Sakano, R
McKinney, B
Khattak, AJ
Rodriguez, DA
Gaskin, C
2007

Many medium and small-size metropolitan areas in the U.S. face increasing traffic problems similar to large metropolitan areas. These metropolitan areas have responded primarily by expanding their road network and capacity. This paper explores the possibility of using a HOT lane in a medium-size metropolitan area for the same purpose. A detailed analysis and a suggested HOT lane solution are prepared for Greensboro-Winston-Salem-High Point metropolitan area. While high congestion are not widespread in the region now, a highway corridor is identified based on forecasted high...