InterMob: a Randomized Controlled Trial Aimed at Reducing Car Use in Regular Car Users

Regular car use is a source of pollution and physical inactivity. InterMob is an interdisciplinary randomized controlled behavioral intervention aiming at reducing car use. The objectives of InterMob are to a) Evaluate the efficacy of a theory- and evidence-based intervention, b) Identify the mechanisms related mobility change, and c) Identify the conditions under which the intervention is effective.

To meet these objectives, 300 regular car users living in Grenoble will be recruited and randomized in one of two arms:

1. experimental group that will receive the InterMob intervention: six months of free public transport/access to a bicycle, and behavior change techniques (personalized transport advice, setting of mobility change goals, considering possible obstacles; 6 months of motivational messages to prompt goal setting and self-monitoring).
2. active control group that will receive information about air pollution (discussion about the health consequences of air pollution, the association between air pollution and car use; 6 months of messages to prompt air pollution monitoring.) Follow-up measures will be carried out until 24 months after the beginning of the study (8-day measurement sessions). Five sessions will involve wearing a GPS/accelerometer, and an air pollution sensor. Participants will complete mobility logs and questionnaires measuring the psychological mechanisms related to their mobility (habits, intentions, self-efficacy), and socio-economical characteristics (number of children, accessibility) during the 8 sessions.

The investigators hypothesize that the participants allocated to experimental group will reduce the car use and increase the use of alternative modes to the car (biking, walking, public transport, and carpooling) more than the participants of the control group, and that these changes will remain. The investigators hypothesize that mobility changes will be mediated by intention and self-efficacy. The investigators hypothesize that the efficacy of the intervention will be moderated by socio-spatial factors (number of children, travel distances) and psychological factors (self-control).

The main criterion will be car use reduction and the use of alternative modes to the car. In addition, the investigators will assess physical activity (minutes of moderate-to-vigorous physical activity), the exposure to air pollution, the quality of life and the carbon footprint associated to transport.

Sample size : The investigators have calculated the sample size considering :

* the proportion of trips made by car (49% of the trips made in Grenoble Metropole are made by car according to the EMD, 2010 which is the most recent survey in the area currently available),
* the potential target population's transport behavior (a percentage of the population can be classified as reluctant drivers with positive attitudes toward other modes of transportation, this population makes 80% of their trips and could potentially reduce their car use to 64% considering the characteristics of the trips)
* the impact of past interventions (car reduction of -17%, from 50% to 33% of car use, Brockman \& Fox, 2011).

The investigators considered a statistical power of 0.8, and a significance level of 0.05 for a proportion of 80% or 50% of trips made by car in the control group. In order to detect a difference of 15% when the share of trips made by car is reduced from 80% to 65% or from 50 to 35%, the investigators need 300 individuals (i.e., 150 individuals in each group).

Eligibility Criteria:
Inclusion Criteria:

* Being at least 18 years old at the time of inclusion

  • Profile: employed / unemployed / retired / on work-study or apprenticeship
  * If employed : Work and live in the SMAAG territory (Metropole of Grenoble + Grésivaudan + Pays voironnais)
  * If in apprenticeship/training program: Working, studying and living in the SMAAG territory (Metropole of Grenoble + Grésivaudan + Pays voironnais)
  * If unemployed / retired : Reside in the SMAAG territory (Metropole of Grenoble + Grésivaudan + Pays voironnais)
* The car/motorcycle/scooter is the main mode of travel during the week (excluding weekends)
* Travels 3, 4, or 5 days by car (excluding weekdays)
* Thinks about reducing car use or has started to reduce car use - Expect to live and work in the Grenoble area in the next 2 years (Very likely and likely options)

Exclusion Criteria:

* Being a student
* Living outside the Metropole of Grenoble + Grésivaudan + Pays voironnais
* Working outside (Metropole of Grenoble + Grésivaudan + Pays voironnais)
* Studying outside (Metropole of Grenoble + Grésivaudan + Pays voironnais)
* Car/motorcycle/scooter is not the main mode of travel
* Travels 0, 1 or 2 days a week by car
* Does not intend to reduce the frequency of car use
* Does not expect to live and/or work in the Grenoble area in the next 2 years