A recent meta-analysis modeled the effects of psychological interventions (called ‘soft interventions’) on car use (1). Most of included studies targeted the perceptions, beliefs, attitudes, values, and norms of participants. Three previous meta-analyses found a small effect size (h ranged from .12 to .16) or no effect on car use reduction (2).

The current meta-analysis included the published paper with a more robust method (i.e., experimental or quasi-experimental design), published in the past 30 years. The aims were to quantify the effect of psychological interventions and to identify the most important moderators. The following moderators were examined with uni-variate models : type of outcomes (e.g., number of trips versus traveled distance), type of intervention (e.g., information + free public transport ticket), psychological variable targeted (e.g., attitudes, habit, knowledge, self-efficacy, social norms), relocated participants, and study design. The authors also examined moderator effect of the percentage of women, incentives, city size by including the psychological variables targeted in models. 

No surprise ! 

Their meta-analysis was based on 41 interventions. They found significant and small effect size (g = 0.163, p < .001, 95% CI [0.11, 0.21]). The most interesting results were in the following findings.  As you can see, the most effective interventions targeted the social cultural and moral norms (g = 0.73), knowledge and awareness (g = 0.348) and those targeting capability and self-efficacy, (g = 0.12). 

The efficacy of interventions targeting relocated car users were not higher than other interventions. The other tested moderators (e.g., % of women) were not significant when the models were adjusted for psychological variables targeted in interventions. 

In conclusion, the decrease of car use after a psychological intervention, expressed in percentages, is approximately 7% ! In other words, the psychological interventions are not the panacea to decrease the car use. The ‘hard interventions’ are, for the moment, the most effective solutions (i.e., altering the physical environment (e.g., closing roads, building bicycle lanes, etc.) or legal or economic policies (e.g., prohibiting car traffic in city centers, congestion pricing, introducing parking fees).  

The future behavioral or psychological interventions should target the social and cultural norms in their interventions. Finally, I think that the academic psychology community should be humbler on this question (3).

• 1. Semenescu A, Gavreliuc A, Sârbescu P. 30 Years of soft interventions to reduce car use – A systematic review and meta-analysis. Transportation Research Part D: Transport and Environment. 2020 Aug;85:102397.
• 2. Arnott B, Rehackova L, Errington L, Sniehotta FF, Roberts J, Araujo-Soares V. Efficacy of behavioural interventions for transport behaviour change: systematic review, meta-analysis and intervention coding. International Journal of Behavioral Nutrition and Physical Activity [Internet]. 2014 Dec;11(1).
• 3. Bernard P. Health psychology at the age of Anthropocene. Health Psychology and Behavioral Medicine. 2019 Jan 1;7(1):193–201.