SWUTC Research Project Description

Title of Project:  A Comprehensive Analysis of Impact of Travel Time Reliability on Congestion Management Strategies

Project Number:  169200

Principal Investigator:
Chandra Bhat
(512) 471-4535
P.I. Affiliation:  University of Texas at Austin
bhat@mail.utexas.edu

Project Monitor:
Johanna Zmud
NuStats LLC Corporate Office
206 Wild Basin Road
Building A, Suite 300
Austin, Texas 78746
Phone: (512) 306-9065
jzmud@nustats.com

Project Status:  Active

Date Started:  9/1/08

Estimation Completion Date:  8/31/09

Estimated Cost - Current Fiscal:  $39,000

Estimated Cost - Total Planned:  $39,000

Project Summary:
Project Abstract:
In this proposal, a general framework will be developed to include travel time reliability in the planning process that can then be employed to improve the consideration of non-recurring congestion effects and operational improvements and strategies. More broadly, the innovation from this proposed high risk, high pay-off, research will provide the tools and techniques needed to support the national strategy to reduce traffic congestion in American urban areas, and will highlight the intricate linkage between operations and planning in congestion management efforts.

Project Objectives:
The goal of the proposed research is to advance analytic tools that are capable of measuring and evaluating travel time reliability improvements of congestion management strategies, and assessing the impacts of such strategies on individual/freight travel decisions.  In evaluating the effectiveness of future reliability improvement projects, it is important to understand and capture the relationships between the projects, the sources of travel time reliability, the travel time variations, and the travelers’ perceived values of, and their behavioral changes in response to, travel time reliability.  Specifically, the objective is to develop a framework to model changes in individuals’ travel patterns due to travel time variability and the resulting travel conditions.  The modeling framework will also account for variations in preferences and sensitivity of travelers, various determinants of travel choices, and a variety of underlying processes for generating variations in travel times.

Task Descriptions:
Task 1.   Literature Review and Development of a Conceptual Framework
In this task, we will examine earlier literature on methods to examine the impact of travel time reliability on travel choices.  We will also develop a conceptual framework identifying the many possible determinants of travel route choice and mode choice, including reliability effects.

Task 2.  Preparation of Data for Analysis
Data for the analysis will be collected using a web-based survey of individuals residing and/or working close to the toll corridors recently opened up in Austin. Respondents will be targeted using several mechanisms that we have used effectively in the past, including seeking the help of Central Austin planning and environmental agencies (such as the CLEAN AIR Force (CAF) of Central Texas, the Central Texas Metropolitan Planning Organization (CAMPO), and the Austin Chamber of Commerce) in informing employers about the survey and asking employers to forward to employees, contacting Austin area residents through a databank of electronic addresses available to us, and disseminating information through radio and TV media outlets to the public at large. Color posters regarding the survey (and including the web link) will also be designed and printed by the University of Texas Design Center, and put up at several geographically dispersed and strategically located public places in Austin. All IRB protocols will be satisfied prior to undertaking the survey. Revealed preference information on travel just before the toll lanes opened in Fall 2007 and after will be combined with a stated preference survey to measure how people perceive reliability when responding to pricing schemes. The stated preference survey will be based on an efficient experimental design with scenarios that are based off the respondent’s revealed choice context.  A small pilot will be conducted to test the survey instruments, the survey procedures and methodology, as well as the control and management of the survey process before conducting the final surveys.

The data generation and assembly will involve (a) the identification of variables likely to affect travel route choice, (b) data cleaning to ensure data consistency, (c) data processing to develop appropriate zone-related variables and impedance variables by time-of-day, mode, and destination, (d) data assembly to bring together all relevant data for each individual trip, and (e) data organization in a format suitable for estimation using the GAUSS matrix programming language.

Task 3. Descriptive Analysis of Travel Choices
This task will entail a descriptive analysis examining activity-travel patterns prior to, and after, the opening of the toll corridor. The results will be presented in the form of tables, histograms, cross-tabulations, pie charts, and other easy-to-understand visual representations.

Task 4.  Formulation of an Econometric Model
The development of a comprehensive analytical structure to examine the travel route choice will be a critical component of this project. Cutting edge methods in discrete choice modeling will be used to combine the before-and-after revealed preference and stated preference responses of individuals, while accommodating for the variations in preferences and sensitivities of travelers. The focus will be on joint route choice (toll versus non-toll) and departure time choice. Values of time and values of reliability for different demographic groups and different activity purposes will be computed, and the relative importance of considering reliability in evaluating pricing options will be assessed.

Task 5.  Model Estimation and Specification Analysis
Models will be estimated in this step using the data assembled in task 2 and the econometric framework developed in Task 4. A number of alternative specifications consistent with theoretical notions (including different variables, different functional forms of variables, and segmentation based on variables such as income levels, race, and residential location) will be compared using formal statistical tests.

Task 6. Assess Policy Implications of the Results
In this task, we will identify how the results of the model estimation can be used to inform policy decision-making and how travel time reliability measures and effects can be accommodated in travel analysis.

Index Terms:
Congestion management systems, Traffic congestion, Travel time, Nonrecurring, Urban areas, Reliability, Research projects