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What we can learn from five naturalistic field experiments that failed to shift commuter behaviour


Across five field experiments with employees of a large organization (n = 68,915), we examined whether standard behavioural interventions (‘nudges’) successfully reduced single-occupancy vehicle commutes. In Studies 1 and 2, we sent letters and emails with nudges designed to increase carpooling. These interventions failed to increase carpool sign-up or usage. In Studies 3a and 4, we examined the efficacy of other well-established behavioural interventions: non-cash incentives and personalized travel plans. Again, we found no positive effect of these interventions. Across studies, effect sizes ranged from Cohen’s d = −0.01 to d = 0.05. Equivalence testing, using study-specific smallest effect sizes of interest, revealed that the treatment effects observed in four out of five of our experiments were statistically equivalent to zero (P < 0.04). The failure of these well-powered experiments designed to nudge commuting behaviour highlights both the difficulty of changing commuter behaviour and the importance of publishing null results to build cumulative knowledge about how to encourage sustainable travel.

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Fig. 1: Forest plot illustrating negligible effects of the five studies by showing the standardized effect size (Cohen’s d) and 95% CI associated with each sample.

Data availability

Coarsened data and modified materials are available at Data and materials have been modified to protect the identity of the partner organization and its employees. Additional materials that do not violate these privacy concerns can be provided on request by the authors.

Code availability

All analyses reported in this study used the statistical software R (v.3.6.1). All R files are available publicly at


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This project received public funding while one of the researchers was employed at the Behavioral Insights Team, but the authors have not received any funding for the writing and publication of this research. We thank the Behavioral Insights Team for their support in writing this paper. Specifically, we thank M. Sanders and L. Costa. The funders provided input into the design of the study but had no role in data collection and analysis, decision to publish or preparation of this manuscript. We also thank S. O’Flaherty and H. Dystrka for their input, and D. Hagmann, J. Roberts and J. Zlatev. for their comments on earlier drafts of this manuscript.

Author information




Data collection and analysis was performed by A.S.K. A.S.K. drafted the original manuscript. A.V.W. provided critical revisions. Both of the authors approved the final version of the manuscript for submission.

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Correspondence to Ariella S. Kristal.

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Supplementary Information

Supplementary Results, Supplementary Notes, Supplementary Discussion, Supplementary Tables 1–4 and Supplementary Fig. 1.


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Kristal, A.S., Whillans, A.V. What we can learn from five naturalistic field experiments that failed to shift commuter behaviour. Nat Hum Behav 4, 169–176 (2020).

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