Ben-Elia, E. and Ettema, D. (2011) Changing commuters' behav- ior ...

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A total of 341 commuters - 221 men and 120 women – chose to participate in the experiment. Upon registration, the participants self selected one out of two types of reward. The first type of reward was an amount of money (3-7 Euros and see next subsection) for each day that the participant avoided driving during the morning rush-hour. In this case, participants were provided with a realistic estimate of how much they could earn in the course of the study. The second type comprised credits towards ultimately keeping a Smartphone (called Yeti) at the end of the experiment. 232 participants (60% men), selected a monetary reward (‘money’) and 109 (74% men) the Yeti reward. The Yeti’s market value was around € 500 at the time. All the participants were inhabitants of the town of Zoetermeer and the vast majority was working at the time in The Hague or its vicinities. They are characterized by relatively high percentage of higher education, moderate to high incomes and mostly families with children. Table 1 presents the descriptives of the participants by group. 3.2 Procedure ***Table 1 about here*** The task and rules were communicated to the participants through the project's back office: Participation had to be voluntary. The participants were to commute at least three times a week from home to work. They had to have access to e-mail and the Internet. They were requested to complete surveys completely and timely. They were made aware that their movements by car would be recorded and had to agree to the installation of an on-board transponder in their car. In addition it was explained that only the car in which a transponder had been previously installed could be eligible for the reward. A travel log (i.e. logbook) was to be filled in daily on a personal webpage on the projects’ internet site. Participants that opted for the Yeti reward were also instructed to switch on the Smartphone during every car trip, in order to get full and easy access to real-time travel information. All communication was to be conducted via the project’s back-office which dealt with complaints or operational problems. A weekly newsletter was also sent to participants’ homes providing further information and clarifications. Participants’ earnings were shown on their personal webpage. The earnings were updated once a week according to the relevant treatment schemes. The monetary rewards were directly paid to participants’ bank accounts at the end of the working week by bank transfer. 3.3 Design Participants were instructed that they could avoid commuting during the morning rush-hour (defined between 7:30-9:30 AM) either by shifting their departure times to earlier or later times of travel, or by choosing other modes of travel (cycling, carpool, public transport), or by working from home (teleworking). The experiment ran for a period of 13 weeks. The first two weeks were without reward (pre-test). The data collected during the pre-test was used to determine participants’ reference travel behavior and subsequent assignment to reward classes. The final week (post-test) was also without rewards. Those participants who opted for money were the subject of three consecutive reward treatments lasting 10 weeks in total: a reward of 3€ (lasting three weeks), a reward of 7€ (lasting four weeks) and a mixed reward (lasting three weeks) of up to 7€ - of which 3€ for avoiding the high peak (8:00-9:00) and an additional 4€ for avoiding also the lower peak shoulders (7:30-8:00, 9:00-9:30). A counterbalanced (blocked randomization) design was used to allocate participants randomly to 6 (that is 3! blocks) possible treatment orders (referred to as scheme). A few exceptions were applied to couples using the same vehicle. The scheme of treatments was communicated to the participants through their personal web 5
pages. Participants in possession of the Yeti could acquire credit during a period of five consecutive weeks. If they earned enough credit relative to a known threshold they could keep the Smartphone. This threshold was determined by their reward class (see below). The other five weeks were without credits but participants could still have access to traffic information. Participants were randomly divided between two schemes in relation to which of the first or second set of 5 weeks credits could be awarded. They were also made aware of their respective schemes. Participants in possession of a Yeti also had 24 hour access to travel information via the handset during 11 weeks: the credit treatment, the no-credit treatment as well as the posttest. This information consisted of real-time travel times on the A12 motorway on the Zoetermeer – The Hague corridor and an online map showing congestion levels on other roads in the area. Information availability was not dependent on the reward itself. In contrast, participants in the money group had access to information available to all other drivers: pretrip through internet and media and en-route from variable message signs along the motorway. In addition to the treatments, each participant was also assigned to a reward class which determined his/her maximum eligible reward. In essence, a participant could only earn the reward as often as he/she was observed to drive in the morning peak during the pre-test. Thus, a participant who would drive in the peak three times per week in the pre-test, could only receive a reward for the third, fourth and fifth day in a week he/she avoided the peak, whereas one who drove in the peak five times per week was eligible for any working day he/she avoided the peak. This reward could be either the daily monetary reward or the threshold number of credits needed to keep the Yeti. It should be noted that retrospectively very few participants failed to meet their threshold. In order to avoid regret, it was also decided at the end of the study to allow all the participants to keep their Yeti’s. Accordingly, each participant was allocated into one of four possible reward classes. Once determined these classes were fixed throughout the rest of the experiment. The majority of participants belonged to classes A and B and the minority to classes C and D. Table 2 presents the number of participants (by gender) in each class. In both groups women are more prevalent in the classes with lower traveling frequencies. For a more detailed description of the experiment’s design see the report (in English) of Knockaert et al., (2007) also available from the authors by request. Self selection of reward types by participants suggests by definition a quasi-experimental design. Like random experiments, quasi-experiments share the same basic principles of manipulation (cause precedes effect) and measurable associations (covariation). In contrast, causation requires more effort as compared to random assignment there are more threats to internal validity. In this we will follow the recommendations of Shadish et al., (2002) noting possible threats. An analysis of threats to internal validity is described in section 4. Lack of a control group also can contribute to validity problems. Several features in the design allow improved control and reduce possible threats. First, the pre-test / post-test design is fostered by additional measurements of stated behavior through the two surveys. Specifically threats resulting from history and novelty can be assessed by comparing between the preliminary survey and the pre-test. In addition, the measured factors from the surveys such as usual behavior, constraints and support measures, can provide relevant mediators to the observed behavior and verify if selection is a problematic issue. This is dealt in detail in Section 4. Second, norm comparisons with traffic counts on the main A12 trajectory suggest other drivers did not change behavior during this period. The sample is small enough not to have any real impact on traffic flow. Since no significant change in traffic occurred during the 13 week observed period we can assert that any difference between observed behaviors with treatments and without is likely to be related to the intervention. In retrospect, it is acknowledged that random assignment and group control would have been the preferred solution. 6
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Page 3 and 4: 1. Introduction Congestion on urban
Page 5: Fourth, do participants’ beliefs
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Page 11 and 12: Mediators (between-subjects factors
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Page 17 and 18: Acknowledgments This study was unde
Page 19 and 20: Kahneman, D., Tversky, A. (1979), "
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Page 23 and 24: Table 4: Results of mixed logistic
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