Publication Detail

Travel Demand Model (TDM) Validation for Ozone Modeling Phase 1 – Exploratory Analysis


Research Report

Suggested Citation:
Niemeier, Debbie A. (1995) Travel Demand Model (TDM) Validation for Ozone Modeling Phase 1 – Exploratory Analysis. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-95-10

Travel demand models (TDM) are usually concerned only with the accuracy of volumes in the peak periods (i.e., AM and PM intervals), off-peak periods and during the average annual weekdays. The relationship between actual traffic ground counts and the simulated volumes is neither accurate nor adequate for more detailed air quality emission models. These models are typically used to generate gridded, hourly specific emissions estimates. To test strategies for improving air quality, the air quality models rely heavily on assigned volumes generated from TDM simulations.

The primary purpose of Phase 1 of this study was to explore statistically based methods for quantifying how well TDM's and their disaggregating factors estimate actual hourly ground counts. Subsequent phases will focus on: 1) developing preliminary mechanisms to calibrate TDMs for optimum accuracy at the required level of detail and 2) exploration of methods for calibrating TDMs from traffic count data and other directional, nonobtrusive measures of travel, which necessarily includes techniques for matching count locations to TDM links. Ultimately, the results of this research will be used to obtain EPA's approval of these methods for validating TDM rather than HPMS (Highway Performance Monitoring System) estimates of VMT as described in 40 CFR Part 51 Section 41.452 Procedures for determining regional transportation-related emissions.