How a Structural Solution to a Real-World Social Dilemma Failed: A Field Experiment on the First Carpool Lane in Europe

In the current field experiment we evaluate a structural solution to a real-life social dilemma by examining the effects of a carpool priority lane on judgments and preferences concerning the decision to commute by carpool (i.e., the presumed cooperative option) or driving alone (i.e., the presumed noncooperative option). Our general hypothesis was that this intervention would evoke a process of self-justification in solo drivers, arising from feelings of relative deprivation andlor cognitive dissonance. Consistent with predictions, we found that in comparison with judgments made before the implementation of the carpoollane, solo drivers tended to decrease the importance of an attribute inherently linked to carpooling (i.e., low travel costs) and to increase the importance of an attribute inherently linked to driving alone (i.e., flexibility). Moreover, solo drivers exhibited a weaker preference for ca/pooling af ter the establishment of the ca/pool lane. This finding suggests that the negative side effects of this structural measure were more pronounced than the intended ca/pool-promoting effects. "The puzzle facing commons [i.e., social dilemma] researchers in the behavioral sciences can be phrased as follows: If technological solutions are often unworkable because of their inherent insufficiencies, or because consumers don't Iike to use them, if changes in morality are difficult to create,... and if egalitarian principles and free choice are to be preserved, how are scarce resources to be saved over extended periods to the satisfaction of consumers?" J. Edney (1980:133) One of the most challenging tasks facing societies and larger groups concerns the * This research was supported by a grant from the