This review focuses on travel behavior change interventions and the Transtheoretical Model of Change (TTM) [1
], a process theory of motivation as the foundation of behavioral change. The review will identify and evaluate the relevant empirical work that has applied the TTM, or parts of the theory, to travel behavior intervention programs. The overall aim is to understand whether, and to what extent, the implemented interventions impact the stages and processes of travel behavior change. The general concepts of the TTM will be explained first to provide a basic understanding of the theory, where it has its roots, and in what contexts it has previously been applied. Then follows an integrative review [3
] of the TTM and travel behavior interventions, as well as the categorizations of these findings. Finally, applications of the TTM to travel behavior change interventions will be discussed, followed by challenges and avenues for future research.
The Transtheoretical Model of Change
Prochaska and DiClemente’s [1
] Transtheoretical Model of Change is well established in health research [4
], as well as being used in travel behavior research [6
]. Compared to attitude/intention-based behavioral models like the Theory of Planned Behavior [8
], the TTM describes behavior change as a sequence of the stages through which individuals progress toward a desired kind of behavior. The TTM consists of two main constructs: the stages of change and the processes of change. The popularity of the TTM is based on its possibility of tailoring interventions to individuals undergoing different stages of change.
The TTM consists of five major stages, as previously described by transport researchers [9
] and illustrated in Table 1
. During the first stage—precontemplation—the individual has no intention of changing his/her behavior and is unaware of the negative consequences of his/her current behavior. Alternatively, he/she believes that these consequences are insignificant. During the next stage—contemplation—the individual is starting to think about changing his/her behavior within the next six months. However, while contemplating, the cost of change is overestimated and the person remains undecided regarding the benefits. During the ensuing preparation stage, the individual is planning to make a change within a month, and has begun taking small steps towards changing. When people reach the action stage, they have recently changed their behavior and are actively trying to modify their (problem) behavior, and to acquire new behaviors. Finally, individuals transition to the maintenance stage once they have been able to maintain a change for more than six months, and are actively trying to prevent a relapse. Relapsing means regressing by one or more stages, which may occur at any stage [6
Behavior is a consequence of a set of processes operating on a number of determinants that can be described as cognitive, affective, and/or behavioral, and assumed to facilitate (or trigger) a transition from one specific stage to the next (see Table 1
]. Interventions, on the other hand, are distinctive measures targeting a specific process. As an example, consciousness raising is a process while interventions for consciousness raising can consist of posters and/or other printed materials. The processes described in Table 1
represent an extended version of the original ten processes identified by Prochaska and DiClemente [1
]. The processes listed in Table 1
, e.g., goal setting, trying new behaviors, and consciousness raising, have all been implemented and tested in health-related research areas, e.g., smoking cessation and condom use [2
]. Depending on the individual stage of change, matching processes are proposed for supporting the individual’s transition to the next stage. For instance, the process of consciousness raising can trigger people into moving from the precontemplation stage to the contemplation stage and, during the process of dealing with different barriers, individuals can move from the preparation stage to action. Below, there is a description, based on the identification of Bartholomew et al. [12
], of linkages between the stages and processes of change (see Table 1
), including examples of interventions targeting a specific process and triggering a transition.
The process of change, i.e., moving from the precontemplation stage to the contemplation stage, involves consciousness raising; that is, finding and learning about new facts, ideas, and ways of encouraging behavior change. The aim is to make individuals aware of the need to alter their current behavior. Dramatic relief can be used to produce enhanced (negative) emotional experiences, followed by reduced affect for the undesired behavior. Interventions used to stimulate dramatic relief include role-plays, personal testimonies, and media campaigns. Environmental reevaluation includes an evaluation of the impact of an undesired behavior on the social environment. Interventions initiating such an evaluation include empathy training, family interventions, and documentaries on the social environment. Both qualitative and quantitative risks are associated with behavior change. Risk assessment involves increased knowledge of: (1) risk comparison (e.g., comparing current negative behavior with future positive behavior) and (2) risk assessment (transactional/short-term probabilities versus cumulative/long-term probabilities of success). Positively-framed interventions encourage a focus on successful behavioral change rather than on failure, likelihood information, personalized messages, and/or facts about the effects of a specific behavior on other people’s aims to alter their risk perception. The process of altering an individual’s perception of the benefits of changed behavior includes interventions focusing on the advantages of the desired behavior and the disadvantages of the (current) risk behavior.
The transition from the contemplation stage to the preparation stage, or even to action, is dominated by cognitive and affective experiential process types. The process of self-reevaluation includes interventions emphasizing that behavioral change is an important part of the individual’s identity, which is basically an assessment of one’s own self-image (e.g., what one wants to be). Interventions like value clarification, healthy role models, and imagery can trigger an individual’s self-reevaluation. Another process during this transition is social support and self-efficacy (interventions allowing skill training), helping individuals cope with the emotional disadvantages perceived to be the result of change. Decision-making focuses on supporting the individual’s process of deciding to change. The tailoring of time horizons includes interventions adjusting the period of time during which the change is to be carried out by the individual. Focusing on important factors emphasizes that aspects of the greatest importance, e.g., important beliefs or consequences, are to be considered. The processes of trying out new behaviors (interventions that can facilitate experiences), persuasion of positive outcomes (interventions altering expectations), and modeling (interventions highlighting role-models who have previously overcome difficult barriers) are aimed at increasing the likelihood of actually making the change.
The transition from preparation to action and from action to maintenance requires behavioral processes in order to facilitate change. For example, self-liberation involves making a firm commitment to change (e.g., a New Year’s resolution or signing a pledge). Skill improvement refers to changing the existing environment in order to reinforce important, obvious, and socially-supported clues. In order not to relapse, it is important to be able to cope with barriers. During this process, barriers are identified and solutions as to how these can be circumvented are developed. Goal setting is an effective process for imposing short- and long-term behavioral change since the individual sets specific and incremental goals. Also highlighting role models creates social reinforcement of the changed behavior (modeling) to the transition to the action stage.
When reaching the action stage, helping relationships can be used to maintain a behavior. Counter conditioning is an intervention that focuses on changing responses to a stimulus. This could mean helping people to react more negatively to something they used to react favorably to (e.g., cigarettes). Contingency management involves rewarding (or punishing) a behavioral change. Stimulus control is a term used to describe situations in which a behavior is triggered by the presence or absence of a stimulus (e.g., if one always eats while watching TV, the eating behavior will be controlled by the stimulus of watching TV). Skill enhancement is aimed at reminding people that setbacks occur and at providing tools for overcoming such situations. Self-rewards are interventions whereby a feeling of success is promoted in order to remind the individual of the positive consequences. When the individual has reached the maintenance phase, the process of coping skills can be used to prevent a future relapse by identifying high-risk situations, developing solutions, practicing these solutions, and coping with setbacks in such a way that the new behavior is maintained.
Over the years, the TTM has become one of the dominant stage models. However, the TTM has also been criticized [6
] for its lack of empirical applicability, for not being clear and consistent regarding which factors influence the transition to the next stage, and for its lack of clarity when it comes to explaining how and why people change. Further, it is argued that the TTM has not been validated when it comes to stage-matched interventions versus mismatched interventions [20
]. One of the main arguments for TTM is its ability to design tailored and individualized interventions. Sutton [20
] emphasizes that this supposedly differentiating factor not only applies to stage models but also to continuum models like the theory of reasoned action [21
]. Even though the TTM has been criticized, it is, nonetheless, popular when it comes to explaining behavioral change in various contexts, e.g., health-related behavior [22
], environmental behavior [4
], organizational change [24
], and consumer behavior [25
]; however, relatively little is known of its applicability in relation to travel behavior change. In the present integrative review, our focus is on the use of the Transtheoretical Model of Change in transport, summarizing the findings and identifying the processes found to support and/or inhibit travel behavioral change.