working paper

A Tool to Evaluate the Safety Effects of Changes in Freeway Traffic Flow

Abstract

This research involves the development of a tool that can be used to assess the changes in traffic safety tendencies that result from changes in traffic flow. The tool uses data from single inductive loop detectors, converting 30-second observations of volume and occupancy for multiple freeway lanes into traffic flow regimes. Each regime has a specific pattern of crash types, which were determined through nonlinear multivariate analyses of over 1,000 crashes on freeways in Southern California. These analyses revealed ways in which differences in variances in speeds and volumes across lanes, as well as central tendencies of speeds and volumes, combine in complex ways to explain crash taxonomy. This research may provide the foundation to forecast the crash rates, in terms of vehicle miles of travel, for vehicles that are exposed to different traffic flow conditions.

working paper

Heterogeneity in Commuters' "Value of Time" with Noisy Data: A Multiple Imputation Approach

Abstract

We estimate how motorists value their time savings and characterize the degree of heterogeneity in these values by observable traits. We obtain these estimates by analyzing the choices that commuters make in a real market situation, where they are offered a free-flow alternative to congested travel. We do so, however, in an empirical setting where several key observations are missing. To overcome this, we apply Rubin’s Multiple Imputation Method to generate consistent estimates and valid statistical inferences. We also compare these estimates to those produced in a “single imputation” scenario to illustrate the potential hazards of single imputation methods when multiple imputation methods are warranted. Our preferred model suggests that the median commuter is willing to pay $30 to save an hour of travel time. However, taking observed heterogeneity into account, median estimates range from $7 to $65 according to varying motorist characteristics.

working paper

Multiply Imputed Sampling Weights for Consistent Inference with Panel Attrition

Publication Date

February 28, 2003

Abstract

This chapter demonstrates a new methodology for correcting panel data models for attrition bias. The method combines Rubin’s Multiple Imputations technique with Manski and Lerman’s Weighted Exogenous Sample Maximum Likelihood Estimator (WESMLE). Simple Hausman tests for the presence of attrition bias are also derived. We demonstrate the technique using a dynamic commute mode choice model estimated from the University of California Transportation Center’s Southern California Transportation Panel. The methodology is simpler to use than standard maximum likelihood-based procedures. It can be easily modified to use with many panel data estimation and forecasting procedures.

Phd Dissertation

High coverage point to point transit (HCPPT): A new design concept and simulation-evaluation of operational schemes.

Publication Date

March 5, 2003

Author(s)

Abstract

This dissertation research proposes the development and evaluation of a new concept for high-coverage point-to-point transit systems (HCPPT ). Overall, three major contributions can be identified as the core of this research: the proposed scheme design, the development of sophisticated routing rules that can be updated in real-time to implement and optimize the operation of such a design, and the implementation of a multi-purpose simulation platform in order to simulate and evaluate such a design under real network conditions. The design is based on Shuttle-style operations with a large number of deployed vehicles under a coordinated transit system that uses advanced information supply schemes with fast routing and optimization schemes. The system design is rather innovative and ensures that no more than one transfer is needed for the travelers, by using transfer hubs as well as reroutable and non-reroutable portions in the vehicles’ travel plans. It yields flexibility for demand-side benefits from options such as price incentives for time-bound “passenger-pooling” at the stops without destination constraints, by the users. A strict optimization formulation and solution for such a problem is computationally prohibitive in real-time. The design proposed in this dissertation is effectively geared towards a decomposed solution using detailed rules for achieving vehicle selection and route planning. If real-time update of probabilities based upon modeling the future dispatch decisions is included, then this scheme can be considered as a form of quasi-optimal predictive-adaptive control problem. Finally, a multi-purpose simulation platform is developed as part of this research in order to evaluate the performance of the system. The final simulations of HCPPT required point-to-point vehicle simulation, which is not possible with off-the-shelf simulators. The simulation framework uses a well-known microscopic traffic simulator that was significantly modified for demand-responsive vehicle movements and passenger tracking. A simulated case study in Orange County showed that with enough deployed vehicles, the system can be substantially better, even competitive with personal auto travel, compared to the often-unsuccessful traditional DRT systems and the existing fixed route public transit. Furthermore, HCPPT can be incrementally implemented by contracting out services to existing private operators.

working paper

Trucking Industry Demand for Urban Shared Use Freight Terminals

Publication Date

February 28, 2003

Abstract

The issue of shared use urban freight facilities first received attention during the 1970’s when it was observed that, while inter-urban freight movements were becoming increasingly efficient, there were significant diseconomies in the movement of freight via truck within urban areas. Early research suggested that shared urban freight facilities should be constructed so that trucking companies could consolidate smaller shipments into larger ones. In the past few years, the concept of “Urban Ports” has gained increasing attention, not just for carriers who need to load and unload freight, but to provide a place near the urban center for truckers to wait out peak traffic periods. In this paper, using recently developed survey data, we examine trucking company interest in such facilities by examining the results of an ordered probit demand model.

working paper

Reducing Risks in Logistics Outsourcing

Publication Date

January 31, 2003

Author(s)

Abstract

Many firms have turned to logistics outsourcing as a way to restructure their distribution networks and gain competitive advantages. Logistics outsourcing in which a third party logistics (3PL) provider is contracted for all or part of an organization’s logistics operations has seen consistently increasing use. Although there are clearly pros and cons of using logistics outsourcing, the full extent of both of these has not been adequately examined. This paper begins to examine some of these risks and discusses some risk reduction measures.

working paper

An Auction Based Collaborative Carrier Network

Publication Date

January 31, 2003

Abstract

In this paper, we examine the for-hire truckload trucking industry in the U.S. and propose a new auction based carrier collaboration mechanism designed to facilitate economically efficient cooperation among functionally equivalent small and medium sized trucking companies based on a post market exchange. An architecture for such a system is proposed and its economic benefits are examined. Analysis shows that the system is a Pareto efficient one in which no participants are harmed and many are better off. The complex decision problems associated with subcontracting, bidding and bid selection in such a system are investigated.

working paper

Traffic Congestion and Trucking Managers' Use of Automated Routing and Scheduling

Abstract

Using data from a 2001 survey of managers of 700 trucking companies operating in California, we tested competing hypotheses about the relationship between managers’ perceptions of the impact of traffic congestion on their operations and their companies’ adoption of routing and scheduling software. Demand for automated routing and scheduling was found to be influenced directly by the need to re-route drivers, and indirectly by the need, generated by customers’ schedules, to operate during congested periods. We were also able to identify which types of trucking companies are most affected by congestion and which types are more likely to adopt such software.

working paper

Evaluation of the California Safe Routes to School Construction Program

Abstract

This report describes the progress made from April, 2002 through January, 2003 in the UC-Irvine evaluation of the California Safe Routes to School construction program. The UC-Irvine research is a pre- and post-evaluation of selected California SR2S sites to determine the effectiveness of physical changes to the local environment in (1) improving the perceived and actual safety of the walk and bicycle trip to school, and (2) enhancing the viability of the walking and bicycling environment. The goal of the research is to assess the impact of the SR2S construction program on pedestrian, bicyclist, and motorist behavior tied to safety, perceived safety, and the amount of non-motorized travel to and from school sites participating in the SR2S program.

This report describes the selection of sixteen school sites, the methods use to collect data at those school sites, and an initial description of the data at the first twelve schools included in this research.