Understanding travel behaviour

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Understanding Travel Behaviour By P.M. Jones, M.C. Dix, M.I. Clarke, and I.G. Heggie. Gower Publishing Company (Old Post Road. Brookfield, VT 05036, USA). ISBN o-566-00606-5, 1983, xviii+281 pp. (tables, figures, bibliography), $36.95(cloth). Gordon Ewing McGill University, Canada This book, the product of a five-year research project by members of Oxford University's Transport Studies Unit, is recommended reading for all researchers who seek to make sense of travel behavior. It also provides an excellent object lesson in research design and execution. The book describes the results of an innovative research project aimed at making up for some of the apparent weaknesses of existing traffic models, including disaggregate travel demand models. At its most detailed level, it examines how family members would respond to changes in school bus schedules by rearranging their travel and activity schedules. The pervading theme is that if we want to understand people's travel decisions, they need to be analyzed in the context of people's total daily activities, particularly the temporal and spatial constraints that some of these activities impose, as well as in the context of the constraints and complications that arise from interdependent behavior in multiperson households. Furthermore, the authors emphasize that the nature of temporal constraints, in particular, means that the response to increased travel time or rescheduled public transport is likely to be discontinuous, contrary to the assumptions of most travel demand models. A difference of 15 minutes might make no material difference to behavior, while a difference of 30 might necessitate major re-arrangements of activity schedules or, given certain family-imposed constraints, may mean that no feasible rescheduling of activities could accomodate the difference. Unlike many travel demand studies that treat behavior from a strong theoretical, but assumption-laden perspective, this book is unashamedly empirical and gets down to the realities of daily life and its multifarious effects on travel decisions. In so doing, it highlights the weaknesses in conventional travel studies, which divorce the travel event from the framework of daily activity which influences it. Another distinguishing feature of the work is that the research design, whose results it reports, was avowedly "exploratory and evolutionary" (research referees and panels please note!). In other words, beyond a certain point in the research as initially proposed, the direction of study, as well as the format for data collection, analysis, and model development was seen as de-

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pending on the results obtained in the initial stages of the study. It is to the credit of the British SSRC that they gave the team a three-year grant on the basis of the relatively imprecise proposal which is helpfully provided in an appendix. Although the subject matter derives from the urban travel demand literature, it does not take too much imagination to see the relevance of their message to recreation and leisure travel research. Leisure travel decisions in terms of trip frequency, destination choice, and activity type are influenced by the same kinds of spatio-temporal constraints and family activity interdependencies as the work, school, and shopping trips which are the stock-intrade of the urban travel literature. We would do well to learn from the lessons of that literature, in which the increased mathematical sophistication of models has not necessarily been repaid by greater success in predicting the effects of transport policy changes. Rather than pursue that path, a recasting of conceptual frameworks along the lines suggested in this book seems justified. Human nature being what it is, those with a heavy intellectual investment in certain styles of mathematical modelling, might try to rationalize why not to make the conceptual shift. Time alone will tell how short-sighted that decision is, and indeed the authors suggest that some hybrid model involving aspects of more traditional utility-maximizing models and their model for rescheduling lists of activities ultimately might be best. Lest it be thought that the arguments put forward are self-serving statements by some non-mathematical social scientists, it is worth noting that Heggie, the principal investigator, is a transport engineer and a leader in the field of mathemtical models of travel demand, while Clarke is a physicist by training, interested in statistical and mathemetical analysis. The book follows the sequence of research so that the reader is in fact led down the same path of discovery as the authors followed. Chapter One provides a cogent explanation of the authors' dissatisfaction with conventional travel demand models, and their inability to accurately forecast the often less-than-expected consequences of public transport improvement schemes. Chapter Two describes a series of small-scale exploratory studies, involving no more than 40 households each, designed to find out how they perceive and articulate their travel behavior. The conclusion is that full activity diaries produce more accurate recall of travel than do diaries of travel alone. Tape recordings of interview sessions also helped highlight various temporal constraints and meshing requirements of household members' activities, issues that play a significant role later in the study. Chapter Three discusses the conceptual significance of viewing travel in the context of activities and chapter Four describes the seven-day activity-travel diary survey

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used in the study area, as well as interesting differences between its reported travel and that found using a purely travel diary survey in the same area. Most of the differences were attributable to the survey method used. Chapters Five to Seven, in which the diary data and in-depth interviews are analyzed, provide descriptions of eight stages in the family lifestyle, each with its prototypical activity-travel pattern. They range from younger adults without children, through families with various In chapter Six, ages of children, to retired persons. the discriminant functions which best explains the variance between the time budgets of households in the different life cycle groups, are shown to involve primarily measures of time spent on child care and on formal work. Life cycle also was found to be the best single discriminator of activity budgets, as compared to other more commonly used descriptors. Chapter Seven provides evidence that life cycle is more than just a proxy for more traditional household descriptor variables. Evidence is also provided of how differences in travel patterns are related to stage in the life cycle, particularly with regard to trip chaining (engaging in several activities on one trip from home) and giving lifts. Chapters Eight through Twelve contain some of the most innovative material. In chapter Eight, the authors present a new survey technique, the Household Activity Travel Simulator (HATS), which comprises a set of display cards used in an in-depth interview, firstly to build up a picture of a family's daily behavior, and secondly to elicit how a policy measure might affect that daily routine. The physical display allows respondents to check the feasibility of any altered activity pattern that they envisage. Chapter Nine describes the use of the technique in four different locales to gauge responses to changes in school hours, and to planned improvements and reductions in various public transport services. One interesting conclusion is that although activity time budgets tended to remain stable in response to policy changes, activity and travel patterns did not. Many activity and travel patterns are found to respond in a discrete and discontinuous manner to changes in transport service, in a way that conventional travel demand models would have difficulty simulating. Furthermore, small adjustments in behavior at certain times of day were perceived as valuable, particularly in-home activities which are normally ignored in policy evaluation. Chapters Ten, Eleven, and Twelve use the understanding of travel behavior obtained from the analysis to develop an algorithm to calculate the feasible set of altered activity schedules for any household faced with a change in its environment. The version described can only handle changes involving schedules. But there is a discussion of the need to extend the algorithm to cover the possible effects of land use changes, such as the siting of new fa-

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cilities, on household activity and travel patterns, and of the need to allow for possible additions, deletions, or reductions in the duration of activities in response to changes in accessibility or the development of new facilities. Despite the depth of treatment of the subject matter, the authors make it clear that there is much scope for improvement in the algorithm to cover more than transport schedule changes. The analytical problems are considerable, but one has a sense that the approach is much more sensitive and appropriate than conventional travel demand If we really want to be able to estimate the models. likely effects of policy decisions on activity and travel patterns, then this route seems to hold promise of eliciting information on the kinds of influences on travel behavior, about which most aggregate and disaggregate travel demand models will probably remain mute. q 0