ITS Berkeley

Asymptotic Approximations for the Transportation LP and Other Scalable Network Problems

Daganzo, Carlos F.
Smilowitz, Karen R.
2000

Network optimization problems with a "scalable" structure are examined in this report. Scalable networks are embedded in a normed space and must belong to a closed family under certain transformations of size (number of nodes) and scale (dimension of the norm). The transportation problem of linear programming (TLP) with randomly distributed points and random demands, the earthwork minimization problem of highway design, and the distribution of currents in an electric grid are examples of scalable network problems. Asymptotic formulas for the optimum cost are developed for the case where...

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.

Moving Bottlenecks: A Theory Grounded on Experimental Observation

Munoz, Juan Carlos
Daganzo, Carlos F.
Taylor, Michael A. P.
2002

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...

Reversibility of the time-dependent shortest path problem

Daganzo, Carlos F.
2002

Time-dependent shortest path problems arise in a variety of applications; e.g., dynamic traffic assignment (DTA), network control, automobile driver guidance, ship routing and airplane dispatching. In the majority of cases one seeks the cheapest (least generalized cost) or quickest (least time) route between an origin and a destination for a given time of departure. This is the “forward” shortest path problem. In some applications, however, e.g., when dispatching airplanes from airports and in DTA versions of the “morning commute problem”, one seeks the cheapest or quickest routes for a...

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...

A Theory of Supply Chains

Daganzo, Carlos F.
2003

This work was stimulated by a comment made by a former student (Prof. Alan Erera of Georgia Tech) in connection with an inventory stabil­ ity game he was going to play in one of his logistics classes. This was the well-known "beer-game" that is often played in business schools to illus­ trate the "bullwhip" effect in supply chains. Al had said to me that he did not have to tell his students how to reorder replacement parts from the other members of the supply chain because he knew from experience that the order sizes the players would generate as the game progressed would become chaotic...