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OCR for page 46
34 I N N O VAT I O N S I N T R AV E L D E M A N D M O D E L I N G , V O L U M E 1 relating to work, school, child care, and eating out can alternatives considered for each choice, and factors or be checked. Unusual time allocations can be examined. attributes considered. This approach would provide an While the structure of travel surveys has tradition- enhanced understanding of individual decision making ally focused on supporting the needs of four-step travel and would move toward behavioral models. models, more information is obtained than is typically Modeling location choices is difficult because of used in the modeling process. Only about 3% of the the large number of alternatives and zones and compli- information obtained from travel surveys is actually used cated substitution structure. Unrealistic modeling in traditional four-step models. The matrix structure of assumptions are typically used, which include considera- the trip distribution and model split submodels of four- tion of all zones and locations. A simple utility combines step models limits the model segmentation and the num- size variables and impedance measures. Using a spatial ber of explanatory variables. Aggregate dependent domain or cognitive map may be a logical approach. In variables include household trip generation, trip distri- terms of activity locations, perceptions of a location may bution, and mode choice by three to four purposes and relate to closeness to home, work, or school. Reasons for two to three time periods. Explanatory variables are typ- the choice of a nonmandatory activity may relate to the ically limited to household size, number of workers, proximity to a routine activity or a unique attraction at number of automobiles, and household income. the location. The role of the activity may be the primary Activity-based models have unlimited segmenta- destination in a travel tour or it may be a secondary stop. tion by travel, person, and household attributes. Variations from the normal work or school location or Activity-based models address logical linkages of activi- schedule could be probed in household surveys. ties and trips of the same person in time and space, as Mode choice causality focuses on whether alterna- well as logical joint activities and travel linkages across tive modes are ever considered or used for the same trip, members of the same household. the reasons for discarding alternative modes, transit reli- New variables could be added to household surveys ability, and automobile reliability. Possible structural to add significant explanatory power to mode and desti- variables include time pressure and the willingness to nation choice portions of travel models. Examples of these pay a toll for time savings, as well as weather-related variables include substituting out-of-home activities with driving conditions. in-home activities related to telecommuting, teleshopping, Attitudinal and stated preference extensions to and telebanking; individual and joint trip substitutions; conventional revealed preference surveys provides one and evening trips. Addressing the use of high-occupancy approach for enhancing current practices. Household vehicles, high-occupancy tolls, managed lanes, toll pay- surveys provide a full picture of daily activity patterns. ment methods, and the toll amount could provide a higher They also provide a good basis for stated preference level of detail about automobile trips. Additional transit extensions to provide a better understanding of choices. trip information might address the sequence of routes and Household surveys remain the main source of data transfers, the use of park-and-ride lots, and the influence needed for travel models. The completeness and the of seat availability, air conditioning, and other amenities. quality of household surveys have been improving. Tech- Mode details might include eligibility for employer- nical fixes have related primarily to questions relating to subsidized parking, parking charges for all trips, the avail- in-home activities and joint activities and travel. Further ability of parking and walking distance to destination, conceptual development associated with activity-based actual automobile availability per trip, and pedestrian and models focuses on causality and decision-making, wider bicycle conditions. Information on income by person, ranges of explanatory variables, and attitudinal and rather than by household would also be of benefit. stated preference extensions. There is a change in the conceptual unit with activity-based models. The four-step model tends to focus on location. A survey would ask the question, USING GLOBAL POSITIONING SYSTEM DATA "What was the next location and associated activity?" TO INFORM TRAVEL SURVEY METHODS Activity-based models focus on activity by asking the question, "What was the next activity and associated Stacey Bricka and Chandra Bhat location?" Focusing on causality represents a construc- tive intermediate stage between the standard outcome- Stacey Bricka discussed the application of Global Posi- based approach and the new process-based approach. tioning System (GPS) technology with travel survey data Causality focuses on why individuals make a specific collection activities. She provided an overview of the use choice or decision. In practical terms, causality is simple of GPS with different aspects of travel surveys and high- and free of chronological details and intermediate steps lighted some of the key findings from these efforts. She of decision making. Short-term model improvements described a recent research project examining the use of could address sequencing and conditionality of choices, GPS with the regional household survey conducted in