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The surprising power of social norms in shifting travel habits.

Peer pressure gets a bad rap, but sometimes a little social shame can work to the greater good. Take a well-known psychology study on the power of social norms: asking hotel guests to reuse their towels for environmental reasons worked a little, but telling them that most other guests in that hotel reused towels worked better, and informing them that most other guests in their same hotel room had done so worked best of all. The approach has worked with household energy use and recycling, too.

Turns out a similar strategy might help reduce car commutes. That's the nutshell conclusion from a recent study conducted by a research trio from the University of Victoria in British Columbia. Led by psychologist Christine Kormos, the researchers found that people who were led to believe their peers had shifted to sustainable commute modes—a so-called "normative intervention"—cut their own driving over time. Here's Kormos and company on their findings:

They imply that normative interventions can perhaps help unfreeze private vehicle use commuting habits by encouraging commuters to consciously evaluate their travel mode choices and to subsequently establish new, more sustainable, habits.

Let's get to the details. The researchers recruited 78 people (average age: 31) who regularly commuted to a college campus near a major city. These study participants kept a daily trip journal for a week to set a baseline of behavior, indicating the number, total time, and mode of the journeys taken. Then they were given information about sustainable transport options (e.g. transit, cycling, carpooling) and asked to reduce their driving trips by 25 percent over the ensuing three weeks.

Here's the twist: not everyone was asked the same way. One group, a control, was simply given the information on alternative modes and nothing more. Another group received a peer pressure message with "low" power, telling them "only" 4 percent of other campus commuters had given up the single-occupancy drive. A third group got the "high" peer pressure push—told that about one in four commuters had switched from a car to a more sustainable travel mode.

Message received. Kormos and colleagues report a clear linear connection between the strength of the normative intervention and the decline in car commutes. Control participants did reduce driving a bit, but participants in the "low" peer pressure group reduced even more, and those in the "high" peer pressure group were by far the most successful—decreasing solo car commutes "by approximately five times, compared with baseline." To the chart:

Commutes by car fell for all groups during the four weeks of the study, but they fell most among those who received a "high" peer pressure message. (Kormos et al., 2015, Environment and Behavior)

Driving did go down slightly for non-commute trips, but not significantly enough to show a clear relationship with the degrees of peer pressure. It's possible that the regional transit system surrounding the test campus, like so many others, is well-equipped for work commutes into the core but less convenient for other types of trips.

The study's chief strength is its quasi-experimental format; this controlled approach makes it pretty clear the normative messages themselves are what actively caused the behavioral change. But there are some drawbacks to the work. All the participants willingly engaged in a trial to reduce driving, so it's possible this was a sample of folks who wanted to be persuaded out of their cars. Isolating participants by geography to see whether the messages had different effects in more suburban settings versus denser city settings might also offer some insight.

A future analysis might also aim to establish a threshold of "high" social pressure. In this study, those participants learned that 26 percent of other similar commuters had reduced their car trips. Would the effect have been measurably greater if they'd been told 50 percent had made the switch? What about 95 percent? Knowing when the effect dropped off could lead to the strongest possible intervention.

The timing of the message will matter, too. As other research has shown, people are most amenable to shifting their travel habits at a moment of major life change—moving to a new home, for instance, or starting a new job. In this case, at least, there's no shame in recognizing when shame is at its peak.

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