Urban and regional planners use travel demand models to estimate changes in transportation activity over time. These models predict the number of trips generated by households as a function of various demographic and socioeconomic considerations and also predict the number of trips attracted to various employment and commercial centers. Estimates for vehicle mode choice, distribution of trip destinations across the metropolitan region, and traffic volumes on various roads also come from these travel demand models. Regional travel surveys, or travel diary studies, are used to collect the data necessary to build travel demand models. Randomly-selected survey participants record trip information over a one-day, three-day, or one-week period. Data collected from thousands of households across the region are then analyzed to develop travel demand models. These regional travel estimates are then used to predict emissions from motor vehicles and serve as primary input data for air regional quality analyses.
Emissions from motor vehicles are directly related to the amount of vehicle activity undertaken. Increased miles or hours of travel results in increased emissions. Emissions are also strongly related to the percentage of dirty vehicles operating in a region. However, even the emissions from "clean vehicles" that normally pass standard smog checks are a function of the way in which the vehicles are operated. Emissions are not only a function of miles driven, but a function of such trip characteristics as time lag between engine starts and the number of hard acceleration activities. Determining the operating characteristics of onroad vehicles is critical to understanding vehicle emissions behavior. Furthermore, some vehicle operating characteristics are likely to be correlated with driver behavior. For example, young male drivers may be more likely to undertake high-speed hard-acceleration activities which significantly increase vehicle emissions. Current emissions models do not take into account driver interaction with the vehicle and vehicle controls because such data are not available for analysis.
To date, vehicle activity studies and travel behavior studies have never been coordinated. This research effort focused on the development of electronic monitoring equipment that would allow such studies to be undertaken jointly. The new equipment will allow simultaneous monitoring of trip characteristics and vehicle and engine operating conditions. Hence, data collected with equipment developed in this research effort will help model developers understand the linkages between travel decisions and vehicle operating conditions. This, in turn, will lead to the development of improved algorithms for predicting emissions as a function of vehicle characteristics, onroad traffic conditions, and household/driver demographics.
A literature review was undertaken to investigate the various aspects of developing an integrated vehicle instrumentation package. Topic areas covered in this review include past and present travel survey methodologies, trends in the field of travel behavior research, results of other vehicle instrumentation studies, availability of useful technologies, survey bias and response rate issues, and traveler route choice studies. One of the greatest benefits of this review was the sharing of research findings among the limited number of researchers currently conducting automated travel diary and vehicle instrumentation studies.
To collect all required data streams for use in travel model development and validation, the integrated vehicle instrumentation package must contain a handheld travel diary, global positioning system, onboard engine monitor, interface computer, and power supply. Because many manufacturers and models within each equipment class had the potential to meet minimum design and performance criteria, the research team first developed a set of system goals in the form of functional specifications. These functional specifications served to narrow the field of potential equipment that would meet project requirements. Given a smaller set of potential equipment solutions, the research team reviewed the detailed technical specifications for the most promising equipment options. The most promising components identified and reviewed were then selected for purchase and field testing.
Each class of equipment was first tested separately to determine superior performers within each class. To facilitate competitive testing, the research team identified those factors that may influence the accuracy and ease of use of each equipment type. With this knowledge in mind, the team then developed standardized test scripts and testing procedures that would challenge the ability of equipment to perform under real-world test conditions. The descriptions of the test metrics and the performance of each individual component are summarized in the test plans and results document. The selection of individual components, final assembly of the prototype system, and software development were based upon these test results.
The final report summarizes the project in its entirety. Information presented in the four previous project volumes is summarized throughout this report. An review of each system component that is in the final prototype package is given, including the original specifications, test plans and results, and final recommendations. The testing of the final prototype unit is summarized in this final report as well. The functionality of the assembled unit is reviewed and shortcomings that must be overcome before such a system is fully deployed are identified.
The literature review and communications with other related research initiatives revealed several problem areas for instrumentation projects. Project development and testing exposed additional issues that should be taken into consideration in future electronic travel diary and vehicle instrumentation research efforts. These problem areas and issues include:
This final report also summarizes the linkage between this project, sponsored by the Federal Highway Administration and Georgia Department of Transportation and the ongoing research effort associated with the development of the year 2000 travel survey in the Atlanta metropolitan region (SMARTRAQ).
Copyright 1998-1999 GeorgiaInstitute of Technology