ITS Berkeley

We study the problem of estimating sparse precision matrices from data with missing values. We show that the corresponding maximum likelihood problem is a Difference of Convex (DC) program by proving some new concavity results on the Schur complements. We propose a new algorithm to solve this problem based on the ConCave-Convex Procedure (CCCP), and we show that the standard EM procedure is a weaker CCCP for this problem. Numerical experiments show that our new algorithm, called m-CCCP, converges much faster than EM on both synthetic and biology datasets.

While the Cell Transmission Model (CTM) is generally accepted as a standard representation of traffic flows on freeways with long links and uninterrupted flows, less is known about the accuracy of CTM or other macroscopic queueing models on urban road networks with short links and frequent flow blockages due to signal control. In fact, almost all existing validations of CTM focus on modeling freeways. In this paper, the authors aim to provide evidence towards selecting the appropriate queueing model dynamics for use in analysis and control of a large-scale network of signalized...

This article considers the dynamic user equilibrium (DUE) problem for parallel networks. The network dynamics are modeled using a Godunov discretization of the Lighthill-Williams-Richards partial differential equation with a trapezoidal flux function. The model is augmented with an additional constraint that prevents vehicle holding which is a flaw in the discretization. The departure rates are assumed to be fixed. Under these assumptions, the authors show that the future allocation of the demand among the different paths at the origin has no effect on the travel time of the vehicles...

This work explores the problem of estimating road link densities from cellular tower signals by mobile subscribers in urban areas. The authors pose the estimation problem as a quadratic program, and present a robust framework that produces vehicle density estimates and is suitable for large-scale problems. The authors demonstrate that both simple and sophisticated models of cellular network connections can be handled robustly by the framework, without sacrificing efficiency or scalability. The authors present a numerical experiment on the I-15 corridor in San Diego based on a...