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88 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 2 shopping street in the town or visiting the closest movie These extensions are not intended to replace SP surveys theater) or was the choice of location based on some with extensive SP games; they are mostly intended to bet- unique properties of the location not associated with any ter the understanding of the observed choices, their nearby area (like visiting Madison Square Garden or sequencing, and the way in which choice sets were formed. Carnegie Hall in New York)? There are several examples of extensions of this sort that could be added to conventional household surveys: Introducing casualty into the modeling framework should naturally reduce the tendency for using simplified For mode and location choices, there can be a ques- models of compensatory utility maximization and work tion asking whether the modelocation was usual or in favor of more elaborate decision-making chains with occasional; partially noncompensatory rules (eliminations). For mode and location choices, there can be guided questions on the reasons behind the choice of a specific mode or destination; ATTITUDINAL AND SP EXTENSIONS For departure and arrival time choices, there can TO CONVENTIONAL RP SURVEYS be a prepared set of answers on questions about how the schedule was actually built, such as "planned in For the foreseeable future, the standard RP household advance" or "occurred in the course of the day out of survey will remain the major source of information for necessity." A different set of questions might be asked at travel demand model estimation. The most satisfactory the end of the survey about the schedule priority of all surveys are those that essentially form travel diaries with activities and whether any schedule adjustment took a full accounting of all daily activity-travel patterns for place to accommodate some other activities in the all household members. This type of survey constitutes schedule. an ideal basis for additional attitudinal and SP-type ques- tions to reflect each traveler's actual situation and is While the authors recognize that not all agencies will much better than a standalone SP survey in which nor- have the budget to support such extensive surveying, it is mally one of the trips or activities is taken out of the also the case that activity-based models can make the daily pattern context and then different questions about biggest advances in the exploration of the sequencing hypothetical alternatives are pivoted off the observed and scheduling of activities at both the individual and choice. household levels. Yet making these advances requires However, the addition of attitudinal and SP questions data that have not conventionally been collected in the to the household survey represents a practical problem context of travel demand surveys and may require new because existing household surveys are generally already innovations in data collection technology. It might well at the upper limits of length and complexity that can be be worth treating these SP extensions as a pilot study or tolerated by interviewees. Thus, it is important to make only collecting the additional data on a subset of the these extensions as easy, natural, and short as possible. households.