Traffic Operations and Management

Ten Strategies for Freeway Congestion Mitigation with Advanced Technologies

Daganzo, Carlos F.
Laval, Jorge
Munoz, Juan Carlos
2002

This report presents ten strategies for improving freeway performance that have become feasible with the advent of new software and hardware technologies for traffic control. Most of the strategies can be applied with advanced implementations of existing hardware. The strategies have in common that they can be rigorously tested. heir measures of performance can be reliably obtained and do not depend on the accuracy of data- hungry, large-scale models.

A Behavioral Theory of Multi-Lane Traffic Flow. Part II: Merges and the Onset of Congestion

Daganzo, Carlos F.
2002

This paper examines the behavior of multi-lane freeway traffic past on-ramps, building on the continuum model of part I and focusing on the onset of congestion. The main complication is that rabbits (fast vehicles) entering from an on-ramp usually stay on the shoulder lane(s) of the freeway for some distance before merging into the fast lane(s). An idealization is proposed, where this distance is taken to be the same for all vehicles. As a result, the system behaves as if there was a fixed buffer zone downstream of the on-ramp where entering rabbits cannot change lanes. The model of part I...

Reproducible Features of Congested Highway Traffic

Smilowitz, K. R.
Daganzo, Carlos F.
2002

Observation of a four-mile long, inhomogeneous, congested traffic stream revealed that vehicle accumulations between detectors vary with flow in a predictable way, and that a macroscopic kinematic wave with a reproducible speed exists in queues despite unusual traffic behavior. As a result, time-dependent vehicle trip times and accumulations inside long queues (and the queue length itself) can be predicted from readily available data without using any “degrees of freedom” to fit the parameters of a model. Experimental vehicle counts were within 20 vehicles of the predictions for over two...

The Bottleneck Mechanism of a Freeway Diverge

Munoz, Juan Carlos
Daganzo, Carlos F.
2002

This paper describes the behavior of multi-lane freeway traffic, upstream of an oversaturated off-ramp. It is based on empirical evidence from freeway I-880 (northbound) near Oakland, CA. The main findings are: FIFO blockage. Even on wide freeways, an off-ramp queue can grow across all lanes and entrap through vehicles in a first-in-first-out (FIFO) system with similar speeds on all lanes and a well-defined kinematic wave (KW). This can hamper freeway flow much more than an on-ramp bottleneck. (In our case the FIFO regime arose a little over 2 km upstream of the exit and reduced discharge...

The Access-Control Problem on Capacitated FIFO Networks With Unique O-D Paths is Hard

Erera, Alan L.
Daganzo, Carlos F.
Lovell, David J.
2002

This paper is concerned with the performance of multicommodity capacitated networks in a deterministic but time-dependent environment. For a given time-dependent origin-destination table, this paper asks if it is easy to find a way of regulating the input flows into the network to avoid queues from growing internally, i.e., to avoid capacity violations. Problems of this type are conventionally approached in the traffic/transportation field with variational methods such as control theory (if time is continuous) and with mathematical programming (if time is discrete). However, these...

Fingerprinting Traffic From Static Freeway Sensors

Munoz, Juan Carlos
Daganzo, Carlos F.
2002

Ask most commuters and they will agree that congestion has reached an intolerable level. To reduce this congestion, engineers need detailed traffic information. Highly detailed information is also prized by traffic scientists, as a prerequisite to improve current traffic theories. Ideally, engineers and scientists would like to obtain from field data the position of each vehicle on a particular facility at every moment in time. The technology to record space-time vehicle trajectories on a massive scale is in its infancy; therefore, analysts must work with much less data. Many freeways are...

Structure of the Transition Zone Behind Freeway Queues

Munoz, Juan Carlos
Daganzo, Carlos F.
2003

Observations of freeway traffic flow are usually quite scattered about an underlying curve when plotted versus density or occupancy. Although increasing the sampling intervals can reduce the scatter, whenever an experiment encompasses a rush hour with transitions in and out of congestion, some outlying data stubbornly remain beneath the “equilibrium” curve. The existence of these nonequilibrium points is a poorly understood phenomenon that appears to contradict the simple kinematic wave (KW) model of traffic flow. This paper provides a tentative explanation of the phenomenon, based on...

Discretization and Validation of the Continuum Approximation Scheme for Terminal System Design

Ouyang, Yanfeng
Daganzo, Carlos F.
2003

This paper proposes an algorithm that automatically translates the "continuum approximation" (CA) recipes for location problems into discrete designs. It is applied to terminal systems but can also be used for other logistics problems. The study also systematically compares the logistics costs predicted by the CA approach with the actual costs for discrete designs obtained with the automated procedure. Results show that the algorithm systematically finds a practical set of discrete terminal locations with a cost very close to that predicted. The paper also gives conditions under...

A Variable Formulation of Kinematic Waves: Solution Methods

Daganzo, Carlos F.
2003

This paper presents improved solution methods for kinematic wave trafficc problems with concave flow-density relations. As explained in part I of this work, the solution of a kinematic wave problem is a set of continuum least-cost paths in space-time. The least cost to reach a point is the vehicle number. The idea here consists in overlaying a dense but discrete network with appropriate costs in the solution region and then using a shortest-path algorithm to estimate vehicle numbers. With properly designed networks, this procedure is more accurate than existing methods and can be applied...