OVERVIEW OF THE RESEARCH AND TASKS

A number of policies designed to alleviate congestion have failed to have the intended or desired effect. While various external factors have been identified as explanations for this, we believe that insufficient attention has been paid to internal reasons, that is to travel-related attitudes and predispositions. A key purpose of this study was to empirically examine the role of travel-related attitudes in an individual's adoption and consideration of various possible strategies in response to congestion. We hypothesized that people who have an intrinsic desire for mobility, and who are currently mobility-deprived, are less likely to adopt travel-reducing strategies (such as telecommuting, changing to a compressed work week) or major lifestyle changes (job or residential relocation, quitting work), and more likely to adopt coping strategies that enable them to maintain or even increase their travel (such as getting a mobile phone or a more comfortable car, changing work trip departure time). We further examined the effect of previous adoption of various strategies the consideration of additional responses, and the demographic distribution of the adoption and consideration of the strategies studied. The result is greater insight into the behavioral response to policies intended to affect travel.

The data for this research come from a 1998 mail-out/mail-back survey of 1,904 residents in three neighborhoods in the San Francisco Bay Area: Concord and Pleasant Hill represent two different kinds of suburban neighborhoods comprising about half the sample, and an area defined as North San Francisco represents an urban neighborhood comprising the remainder. The questions in the survey were classified into 11 categories of variables: objective mobility, subjective mobility, relative desired mobility, traveling liking, travel attitudes, personality, lifestyle, excess travel, adoption and consideration of travel-related strategies, mobility constraints, and demographic characteristics. For this study, we chose to focus on commuting workers since they contribute most heavily to peak-period congestion, and are likely to be the most active in the adoption and consideration of travel-related strategies; the subset of 1,283 cases that consists of commuting workers with relatively complete responses to key questions is used in this analysis. Binary logit models were developed for the consideration of each of 16 individual travel-related strategies.

KEY RESULTS

Objective mobility: Objective mobility variables are generally positively associated with the consideration of the travel-related strategies presented in this study. The more an individual travels for short distance, the more likely she is to consider the low-cost travel-maintaining/increasing strategies. Whether the large amount of short-distance travel is by necessity or by choice, the low-cost travel-maintaining/increasing strategies offer appealing options for making that travel more pleasant or productive. On the other hand, a higher frequency of short-distance travel does not necessarily mean a longer total travel distance; it is not the frequency but the distance of short-distance travel that has a more important impact on the consideration of the medium- or high-cost travel-reduction strategies.

Subjective mobility: Generally, short-distance subjective mobility variables are positively associated with the consideration of the travel-related strategies. The effect of subjective mobility on the consideration of the travel-related strategies is quite similar to that of objective mobility.

Relative desired mobility: Individuals wanting to decrease their travel are more likely to consider travel-maintaining/increasing strategies (perhaps to lighten the burden of undesired but necessary travel); competing preferences (the desire for more travel in one category motivates consideration of a strategy that will reduce another kind of travel, namely commuting – presumably to make more time for the desired type of travel) may motivate individuals to consider travel-reducing and major location/lifestyle change strategies (e.g., those wanting more travel are more inclined to consider commute-reduction strategies).

Travel liking: Liking short-distance travel for entertainment and liking long-distance travel overall increase the probability of considering the travel-maintaining/increasing strategies.

Travel attitudes, personality and lifestyle: The attitude, personality and lifestyle factors that most commonly, and positively, affect the consideration of the travel-related strategies are pro-environmental solutions (attitude), adventure seeker (personality) and frustrated (lifestyle). Individuals advocating environmental protection are more likely than others to consider reducing their commute and/or minimizing solo driving to decrease their personal energy consumption and impacts on the environment. Also, they are more likely to consider getting a fuel efficient car to decrease their fuel consumption. Compared to others, such individuals are more susceptible to a change. The adventure seeker factor score has a positive impact on the consideration of several different strategies in all three conceptual categories. The frustrated factor score is significant in five models. Individuals who are frustrated may view travel-related strategies as potentially one way to increase their control and/or life satisfaction.

Mobility constraints: Mobility constraints increase the probability of considering the travel-related strategies in all three conceptual bundles. It is noteworthy that limitations on driving during the day and lower vehicle availability are each significant in four models, and that these two constraints are more likely to affect the consideration of the workstyle adjustments. This suggests that a desire to shorten the commute is an important motivation for individuals with such constraints to consider these travel-related strategies.

Demographics: Age-related variables (age category and years lived in the U. S.) appear most commonly in the models. Their generally negative effects indicate that older people are less likely to consider most of these strategies. In these models, year of personal vehicle is only (and, logically, negatively) associated with the auto improvement strategies. Individuals having dependents to care for are more inclined to acquire more temporal and/or spatial flexibility to better provide the necessary care. Higher personal and household incomes either directly or indirectly have a positive impact on the consideration of travel-related strategies.

Former adoption of travel-related strategies: Apart from “Change jobs closer to home”, the former adoption of each of the remaining 15 individual strategies significantly affects the consideration of the same strategy. On one hand, among the 15 strategies, the former adoption of getting a mobile phone, getting a better car, and getting a fuel efficient car are negatively associated with their respective reconsiderations, implying that the former adoption is still in force and the individual is enjoying the utility of such an adoption. On the other hand, the former adoption of each of the other 12 strategies has a positive impact on its reconsideration. Either the individual is enjoying and still wants to enjoy the benefits from the former adoption, or such strategies are attractive again as circumstances change. Given that these strategies are adopted once, it is natural that they would be adopted repeatedly over a person’s working life. Whenever time since adoption of a strategy is significant to the reconsideration of the same strategy, it appears with the opposite sign to that of the binary former adoption variable, meaning reinforcement rather than counteraction of the former adoption variable. In addition, the effects of three pairs of former adoption variables on the consideration of another strategy follow the same pattern as those of former adoption variables on the consideration of the same strategy, indicating that the adoption of one strategy is more likely to trigger the consideration of the other related strategy in the short term. When the former adoption of a strategy is significant, its dominant effect on the consideration of another strategy is positive: the former adoption of i increases the probability of considering j. Complementary effects are obviously exhibited in the home-based work bundle. The former adoption of each of the strategies in the alter employment bundle does not affect the consideration of any other strategies studied here, suggesting that working part-time and quitting work are likely to be the most radical and exhaustive changes to cope with congestion. Although not as radical, mode change strategies are also isolated in their nearly complete lack of influence on the consideration of other strategies (with the exception, ironically, that changing to driving alone has a negative influence on the consideration of changing to part-time work). Although the former adoption of changing jobs closer to home does not significantly affect its reconsideration, it frequently appears with a positive coefficient in models of the consideration of other strategies; conversely, the former adoption of “Move your home closer to work”, which is in the same bundle as the employment relocation, is only significant in the model of its own reconsideration. This may imply that, in contrast to a new residential location, some aspects of a new job (e. g. a higher salary, increased flexibility) offer individuals an opportunity to seek other kinds of changes, which, of course, may not only be for transportation reasons.

Finally, the key findings provide evidence in support of our initial hypotheses. A more detailed comparison of some of these hypotheses and results is summarized in Table 1.

In conclusion, the consideration of travel-related strategies is affected not only by the amounts of travel that individuals actually did, but also by their subjective assessments, desires, and affinities with respect to travel. Generally, objective mobility is positively associated with the consideration of these strategies, and the effects of subjective mobility on the consideration are similar to those of objective mobility. However, the influences of relative desired mobility and travel liking are somewhat more complex. In contrast to objective mobility, relative desired mobility tends to negatively affect the consideration of these strategies in general, but there still exist some plausible positive effects on consideration (referred to as competing preferences). The influences of travel liking seem to be diverse although it consistently positively affects the consideration of low-cost strategies. In a word, this study helps us further understand the influences of these mobility-related variables on the consideration of each strategy. However, the effects of objective mobility, subjective mobility, relative desired mobility and travel liking are always intertwined in individuals’ choice processes, which contribute to the substantial diversity of their responses. Further, since it is objective mobility that is often the basis of public policy, these relationships imply that individuals may not respond to public policies designed to adjust their behaviors in the way that policy makers expected. An individual’s travel attitudes, personality, and lifestyle play an important role in her consideration of travel-related strategies. The frequent appearances of these factors further illustrate how different people respond to congestion, and hence provide helpful information to better understand individuals’ diverse behaviors. However, it is difficult for policy makers to acquire such information for various reasons. An individual’s past experience greatly affects her consideration of travel-related strategies. In the current study, there is evidence that (1) the former adoption of a strategy, and sometimes the time since adoption as well, has an important impact on the consideration of the same strategy, with a positive association dominating; and (2) the adoption of one strategy sometimes triggers the consideration of another related change in the short term. These findings suggest that the effectiveness of public policies is impacted by individuals’ past experiences. Finally, demographic characteristics may affect the response to public policies.

The single key theme that underlies the results of this study is that individuals’ responses to the travel-related strategies analyzed here – many of them directly tied to public policies intended to reduce vehicle travel – are influenced by a large variety of qualitative and experiential variables that are seldom measured and incorporated into demand models. Although there are challenges associated with that measurement and incorporation, those challenges are not insurmountable. Devoting further efforts to understanding the role of these attitudinal, personality, lifestyle, and experience variables will improve our ability to design effective policies and to accurately forecast the response to policy interventions as well as natural trends.

Table 1: Summary of Hypotheses and Results

Variable type	General hypotheses	Results
Objective mobility	(1) The more individuals travel, the more likely they would be to consider all travel-related strategies, including the travel-maintaining/increasing ones.	(1) Our findings support this hypothesis.
Subjective mobility	(1) A higher subjective mobility is positively associated with the consideration of a wide range of travel-related strategies.	(1) Our findings support this hypothesis, similarly to objective mobility.
Relative desired mobility	(1) Individuals having a higher relative desired mobility are more likely to consider travel-maintaining/increasing strategies, and (2) less likely to consider travel-reducing and major location/lifestyle change strategies.	(1) Our findings are counter to this hypothesis, indicating that these strategies are more favored by those wanting to decrease their travel (perhaps to lighten the burden of undesired but necessary travel); (2) Our findings provide some support for this hypothesis. However, competing preferences may affect the direction of an individual’s consideration (e.g., those wanting more travel are more inclined to consider commute-reduction strategies).
Travel liking	(1) The more individuals like travel, the more likely they would be to consider travel-maintaining/increasing strategies, and (2) the less likely they would be to consider travel-reducing and major location/lifestyle changing strategies.	(1) Our findings provide some support for this hypothesis; (2) Our findings fail to support this hypothesis, perhaps again due to competing preferences.
Travel attitudes	(1) Individuals with attitudes favoring travel would be more likely to consider travel-maintaining/increasing strategies, while (2) those with attitudes not favoring travel would be more likely to consider travel-reducing and major location/lifestyle change strategies.	(1)(2) Our findings provide support for these hypotheses although some travel attitude factors do not often appear in the models, and others do not appear at all.
Personality	(1) The adventure seeker factor is positively associated with the consideration of most travel-related strategies.	(1) Our findings support this hypothesis.
Lifestyle	(1) The family/community-oriented factor is positively associated with the consideration of travel-reducing and major location/life style change strategies; (2) Being frustrated is positively related to considering a wide range of travel-related strategies; (3) A positive score on the workaholic factor positively affects the consideration of the strategies beneficial to work; (4) Status seekers may be more inclined to consider strategies involving material acquisition.	(1) Our findings provide some support for this hypothesis; (2) Our findings support this hypothesis; (3) Our findings fail to support this hypothesis; (4) Our findings provide some support for this hypothesis.
Excess travel	(1) Excess travel plays an important role in the consideration of a wide range of travel-related strategies.	(1) Our findings fail to support this. However, the effects of the excess travel indicator may be captured by the adventure seeker factor and the mobility variables.

(Table 1 continued)

Variable type	General hypotheses	Results
Mobility constraints	(1) Mobility constraints positively affect the consideration of a variety of travel-related strategies.	(1) Our findings support this hypothesis.
Demographic	(1) Females are more likely to consider the more costly, travel-reducing and major location/lifestyle change strategies; (2) Those in upper income categories are more able and therefore more likely to consider a wide range of travel-related strategies.	(1) Our findings fail to support this hypothesis, although gender effects may be partly captured by other variables in the models; (2) Our findings offer mixed (direct and indirect) support for this hypothesis.
Strategy adoption	(1) The former adoption of a strategy could be either positively or negatively associated with the consideration of other strategies; (2) The former adoption of a strategy positively affects the consideration of the same strategy; (3) The time since adoption of a strategy is positively related to its reconsideration.	(1) Our findings support this hypothesis; (2) Our findings generally support this hypothesis although the effects of three strategies are counter to it (for logical reasons) and the effect of one strategy is not significant; (3) Our findings fail to support this hypothesis. Conversely, we found that the time since adoption of a strategy appears with the opposite sign to that of its former adoption.

REFERENCES

Cao, Xinyu and Patricia L. Mokhtarian (2003) Modeling the Individual Consideration of Commute-Oriented Travel Strategies. Research Report, Institute of Transportation Studies, University of California, Davis, in progress.

Choo, Sangho and Patricia L. Mokhtarian (2003) Modeling the Consideration of Bundles of Travel-Related Strategies. Research Report, Institute of Transportation Studies, University of California, Davis, in progress.

Clay, Michael J. and Patricia L. Mokhtarian (2002) Personal travel management: The adoption and consideration of travel-related strategies. Paper presented at the Association of Collegiate Schools of Planning conference, November 2002, and submitted to Transport Policy.

Clay, Michael J. and Patricia L. Mokhtarian (2002) The Adoption and Consideration of Commute-Oriented Travel Alternatives. Research Report UCD-ITS-RR-02-04, Institute of Transportation Studies, University of California, Davis, September.

Available at www.its.ucdavis.edu/publications/2002/RR-02-04.pdf .