Spillover effect of congestion charging on pro-environmental behavior

This paper reports an examination of a spillover effect from a real-world intervention policy of traffic congestion charging that impacted various pro-environmental behaviors. A mailed questionnaire surveyed randomly sampled car owners living in Stockholm County (Sweden) to gather data on travel modes and pro-environmental behavior before and after the introduction of a trial congestion charging policy in Stockholm. Results of paired t test on 291 valid samples revealed that this policy not only directly mitigates traffic congestion (i.e., a direct effect of the policy intervention), but it also indirectly ‘spills over’ to affect pro-environmental behaviors in nontransportation situations (resource and energy use). A spillover to pro-environmental behavior was confirmed by respondents who shifted their travel mode from car to pro-environmental travel mode. Interestingly, the spillover was also confirmed in a group of respondents who remained in the pro-environmental travel mode and others who adversely shifted away from a pro-environmental travel mode to cars. Results suggest that the spillover effect from an environmental policy intervention can have considerable impact on facilitating pro-environmental behaviors and surrounding issues in more general contexts, thus warranting careful evaluation with a wider perspective.