Patricia L. Mokhtarian

How derived is the demand for travel? Some conceptual and measurement considerations

This paper contests the conventional wisdom that travel is a derived demand, at least as an absolute. Rather, we suggest that under some circumstances, travel is desired for its own sake. We discuss the phenomenon of undirected travel – cases in which travel is not a byproduct of the activity but itself constitutes the activity. The same reasons why people enjoy undirected travel (a sense of speed, motion, control, enjoyment of beauty) may motivate them to undertake excess travel even in the context of mandatory or maintenance trips. One characteristic of undirected travel is that the destination is ancillary to the travel rather than the converse which is usually assumed. We argue that the destination may be to some degree ancillary more often tan is realized. Measuring a positive affinity for travel is complex: in self-reports of attitudes toward travel, respondents are likely to confound their utility for the activities conducted at the destination, and for activities conducted while traveling, with their utility for traveling itself. Despite this measurement challenge, preliminary empirical results from a study of more than 1900 residents of the San Francisco Bay Area provide suggestive evidence for a positive utility for travel, and for a desired travel time budget (TTB). The issues raised here have clear policy implications: the way people will react to policies intended to reduce vehicle travel will depend in part on the relative weights they assign to the three components of a utility for travel. Improving out forecasts of travel behavior may require viewing travel literally as a “good†as well as a “bad†(disutility).

Examining the Impacts of Residential Self-Selection on Travel Behaviour: A Focus on Empirical Findings

Abstract Numerous studies have found that suburban residents drive more and walk less than residents in traditional neighbourhoods. What is less well understood is the extent to which the observed patterns of travel behaviour can be attributed to the residential built environment (BE) itself, as opposed to attitude‐induced residential self‐selection. To date, most studies addressing this self‐selection issue fall into nine methodological categories: direct questioning, statistical control, instrumental variables, sample selection, propensity score, joint discrete choice models, structural equations models, mutually dependent discrete choice models and longitudinal designs. This paper reviews 38 empirical studies using these approaches. Virtually all of the studies reviewed found a statistically significant influence of the BE remaining after self‐selection was accounted for. However, the practical importance of that influence was seldom assessed. Although time and resource limitations are recognized, we recommend usage of longitudinal structural equations modelling with control groups, a design which is strong with respect to all causality requisites.

Self-selection in the relationship between the built environment and walking: Empirical evidence from Northern California

Abstract Available evidence establishes correlations between the built environment and walking, but not a causal relationship, leading researchers to debate whether “self-selection” explains the observed correlations: do residents who prefer to walk choose to live in more walkable neighborhoods? Using data from a survey of residents of eight neighborhoods in Northern California, this article presents new evidence on the possibility of a causal relationship between the built environment and walking behavior. This work improves on most previous studies by incorporating travel attitudes and neighborhood preferences into the analysis of walking behavior, and by using a quasi-longitudinal design to test the relationship between changes in the built environment and changes in walking. Both analyses show that the built environment has an impact on walking behavior even after accounting for attitudes and preferences.

A Typology of Relationships Between Telecommunications And Transportation

This paper defines the relationship between telecommunications and transportation, by expanding on linkages already identified in the literature, by identifying additional relationships, and by putting these relationships into a robust conceptual framework. There are conceptual, physical, analytical, and regulatory parallels between telecommunications and transportation. Telecommunications affects the demand for, and supply of, transportation — and vice versa. In the broadest sense, all communication requires transportation in order to occur: transportation either of people, of objects, or of electronic impulses. In other words, communication takes place via one or more of those three modes. It is suggested that communication breeds communication. That is, the easier it is to communicate (whether through travel or communications), or the more that one or another form of communication takes place, the more that communication as a whole is stimulated. The relative shares of each of the three modes of communication may vary as one mode partially substitutes for another, but the absolute amounts of communication via each mode are likely to increase. Two empirical studies are summarized, one illustrating that teleconferencing increased travel, the other illustrating that telecommuting decreased travel. Other implications for transportation planning are highlighted.

A Synthetic Approach to Estimating the Impacts of Telecommuting on Travel

A multiplicative model is proposed as a framework for examining the current knowledge in forecasting the demand for telecommuting and the resulting transport impacts. A running illustrative example (containing a base and a future case) is developed, using plausible values for each factor in the model. The base case suggests that 6.1 per cent of the workforce may be currently telecommuting, with 1.5 per cent doing so on any given day, eliminating at most 1 per cent of total household vehicle-miles travelled. Future reductions could be smaller as commute distances of telecommuters become more average and as the stimulation effect of telecommuting grows. In any event, it is likely that—due to counteracting forces—the aggregate travel impacts will remain relatively flat into the future, even if the amount of telecommuting increases considerably.

Telecommunication and Travel: The Case for Complementarity

The potential of telecommunications to substitute for travel has long been appreciated. Indeed, such potential has often been not just a later realization but an integral impetus behind the development of the technology. Early communication devices such as jungle tom-tom drums, trumpet alarms, smoke signals and flashing lanterns were surely conceived precisely to replace the need for a physical messenger. The same cannot necessarily be said of the more recent (1876) invention of the telephone. Alexander Graham Bell’s own initial vision of its uses seemed to be more along the lines of broadcast radio than personal communication, while the President of Western Union dismissed it as an “electrical toy”, and the Chief Engineer of the British Post Office in 1879 sniffed that the “superabundance of messengers, errand boys, and things of that kind” in Great Britain obviated the need for the telephone there (Dilts 1941). However, it did not take long for speculation to begin about the potential of the new technology to eliminate travel. Albertson (1980) refers to a letter to the editor of the Times published May 10, 1879 suggesting that the telephone could provide relief from travel for harried businessmen

Modeling the desire to telecommute: The importance of attitudinal factors in behavioral models

This paper begins to operationalize a previously published conceptual model of the individual decision to telecommute. Using survey data from 628 employees of the City of San Diego, hypothesized drives to telecommute and constraints on/facilitators of telecommuting are measured. A binary logit model of the preference to telecommute from home is estimated, having a p2 of 0.68. The explanatory variables include attitudinal and factual information. Factor analysis is performed on two groups of attitudinal questions, identifying a total of 17 (oblique) factors which can be classified as drives and constraints. Additional measures are created from other data in the survey, usually objective sociodemographic characteristics. Variables representing at least four of the five hypothesized drives (work, family, independence/leisure, and travel) are significant in the final model. Variables from four of the ten groups of constraints (job suitability, social/professional and household interaction concerns, and a perceived benefit of commuting) are significant, primarily representing internal rather than external constraints. The results clearly demonstrate the importance of attitudinal measures over sociodemographic ones, as the same demographic characteristics (such as the presence of children, commute time) will have different effects on preference for different people.

TELECOMMUTING AND TRAVEL: STATE OF THE PRACTICE, STATE OF THE ART

This paper provides an overview of the status of telecommuting in the United States, especially as it relates to changes in travel behavior. Regarding the state of the practice, the paper discusses some refinements to the definition of telecommuting that have developed through increased operational experience. It reports several policy statements involving telecommuting, and explores the appeal of telecommuting as a public policy instrument. It highlights some trends in the implementation of home-based and work center-based telecommuting, and suggests that visible public-sector involvement has been crucial to the increased activity in this area.In sketching the state of the art, the paper outlines some frequently-stated hypotheses on telecommuting and travel behavior, and summarizes current empirical findings relating to those hypotheses. Finally, it suggests a variety of topics suitable for further research. These include studying factors influencing the ultimate adoption levels of telecommuting; impacts on energy/air quality, mode choice, and location/urban form; interactions with other transportation demand management strategies; relationships to the traditional urban travel demand forecasting process; cost/benefit tradeoffs; and telecommuting centers.

Modeling the choice of telecommuting: setting the context

In this paper a conceptual model of the individual decision to telecommute is presented. Key elements of that decision, including constraints, facilitators, and drives, are defined and the relationships among them described. The major types of constraints (if negative) or facilitators (if positive) include external factors related to awareness, the organization, and the job, and internal psychosocial factors. The major types of drives are work, family, leisure, ideology, and travel. It is argued that the absence of constraints is a necessary but not sufficient condition for telecommuting to be adopted by an individual. The presence of one or more drives, assumed to be associated with some dissatisfaction, is necessary to activate the search for a solution to that dissatisfaction. The choice set contains those alternative solutions perceived to be feasible by the individual. It may or may not contain telecommuting (depending on whether all constraints are nonbinding or not), and probably contains other alternatives having nothing to do with telecommuting. Each alternative is evaluated in terms of how effectively it satisfies the drive, and the individuals attitudes toward it. The alternative (or bundle of alternatives) which maximizes individual utility becomes the preferred behavioral pattern. However, short-term constraints may prevent the preferred behavior from being chosen. The process is a dynamic one, in which previous choices affect attitudes and constraints and alter drives. Work directed by the authors is under way to operationalize the conceptual model.

The impact of gender, occupation, and presence of children on telecommuting motivations and constraints

Accurate forecasts of the adoption and impacts of telecommuting depend on an understanding of what motivates individuals to adopt telecommuting and what constraints prevent them from doing so, since these motivations and constraints offer insight into who is likely to telecommute under what circumstances. Telecommuting motivations and constraints are likely to differ by various segments of society. In this study, we analyze differences in these variables due to gender, occupation, and presence of children for 583 employees of the City of San Diego. Numerous differences are identified, which can be used to inform policies (public or organizational) intended to support telecommuting. Most broadly, women on average rated the advantages of telecommuting more highly than men – both overall and within each occupation group. Women were more likely than men to have family, personal benefits, and stress reduction as potential motivations for telecommuting, and more likely to possess the constraints of supervisor unwillingness, risk aversion, and concern about lack of visibility to management. Clerical workers were more likely than managers or professionals to see the family, personal, and office stress-reduction benefits of telecommuting as important, whereas managers and professionals were more likely to cite getting more work done as the most important advantage of telecommuting. Constraints present more strongly for clerical workers than for other occupations included misunderstanding, supervisor unwillingness, job unsuitability, risk aversion, and (together with professional workers) perceived reduced social interaction. Constraints operating more strongly for professional workers included fear of household distractions, reduced social and (together with managers) professional interaction, the need for discipline, and lack of visibility to management. Key constraints present for managers included reduced professional interaction and household distractions. Lack of awareness, cost, and lack of technology or other resources did not differ significantly by gender or occupation. Respondents with children rated the stress reduction and family benefits of telecommuting more highly than did those with no children at home. Those with children were more likely than those without children to be concerned about the lack of visibility to management, and (especially managers) were more likely to cite household distractions as a constraint.