Nudging for Sustainable Mobility



The transportation sector is the largest producer of greenhouse gasses in the United States, according to the Environmental Protection Agency. Over half of those emissions come from light-duty vehicles, like passenger cars and four-wheel trucks. In order to combat the dangerous effects of vehicle emissions, cities are introducing more sustainable transit options, like electric buses and cable cars. Yet these new, green modes of transportation won’t help the environment if potential users don’t utilize them.

To encourage residents to adopt greener transit, some cities are applying theories of behavioral economics. Nudges are non-intrusive interventions that guide people toward a desirable action; in their 2008 book Nudge, Richard Thaler and Cass Sunstein explain that a nudge “is any aspect of the choice architecture that alters people’s behavior in a predictable way without forbidding any options or significantly changing their economic incentives.” Choice architecture is another way of saying the context in which choices are presented. Thaler and Sunstein are careful to point out that “nudges aren’t mandates.” Encouraging one option over another is acceptable, but banning one option isn’t.

So when there are multiple transit options, individuals have a choice of how to get from Point A to Point B. But how do they decide which one to take? Research into travel behavior reveals how much psychological and social factors influence transit choices; attitudes about public transit, established travel habits, and loss aversion can all lead individuals to exhibit non-rational behavior when planning their transportation. This is in contrast to the traditional “rational man” theory of economics that has previously been applied to transit. The new research shows that there is an opportunity for cities to step into the choice architecture and nudge people toward greener modes of transit. Below are three examples of how cities have combined behavioral insights with new technology and data to increase green transit usage and decrease greenhouse gas emissions.

Bike commuter

Driving Less in Durham

In Durham, North Carolina, city officials wanted to nudge commuters out of their single-occupancy cars and toward more sustainable options. So for six months in 2018, Durham used two different behavioral economic strategies to encourage 1,500 downtown workers to leave their cars at home. For the first strategy, participants provided their home and work addresses, and opted into receiving personalized maps with bike, bus, and walking routes. The emailed maps compared the trip times and reminded workers that they could save gas money and increase their physical activity if they didn’t drive. The maps also included some social norms influencing, by declaring that driving downtown was “so 2017.” This nudging worked better than the city initially expected, as employees who took part in the pilot were 12 percent more likely to use alternative methods of transit than the employees who didn’t have the nudge.

The second intervention was for city employees, and not only nudged them toward more sustainable transit options but also rewarded them for choosing the bus over driving alone. The GoDurham bus lottery meant that bus riders were able to enter a weekly lottery with a cash prize. Commuters that participated in the weekly bus lottery “reported commuting by [car] alternatives 19 percent more, and reported a higher level of happiness and lower levels of stress during the pilot.” Based on the success of these two pilots, the City of Durham was awarded $1 million in the Bloomberg Philanthropies U.S. Mayors Challenge competition; they will spend the next few years continuing to nudge residents toward healthier, greener transit.

Transit Interventions in Vancouver

In Canada, four out of five commuters use private cars to get to work, and less than a quarter of residents in Toronto and Vancouver take public transit to work, despite having access. Translink, the Metro Vancouver transportation network, wanted to apply behavioral insights to increase the demand for alternative and sustainable modes of transit. Translink partnered with Alta Planning and Design and the Behavioral Insights Team (BIT) to design and report on a program that would increase public transit use.

The team’s approach had three stages. First, mapping out the behavioral touch points where transit choices could be influenced. Second, designing an “easy, attractive, social, and timely” intervention. And third, testing to see whether the intervention worked. The interventions, or nudges, would be different for different groups of people. Low-frequency users would be encouraged to “Try it Again” while mid-frequency users were asked to “Make it a Habit.” High-frequency users were told to “Use it Well.”

For the “Try it Again” group, the researchers identified various psychological barriers “preventing infrequent or inexperienced users from giving public transportation a try.” These included status quo biases, ambiguity aversion, and the perception of cars as status symbols. In order to address the various blocks and biases, the researchers created multiple interventions. Researchers knew that individuals are likely to change one habit if they are going through a transition period. Sending a message about a new sustainable route can spark a transportation behavior change right after a move. Trip uncertainty is reduced and people are less frustrated and anxious about their commute when scheduled train times are shared by text or real time locations are shared in an app. Additionally, combating negative stereotypes can make public transit a more viable option for the low frequency riders.

The “Make it a Habit” group is familiar and comfortable with public transit, but doesn’t ride with high frequency. In Metro Vancouver, 11 percent of the population falls into this mid-frequency group; their frequency of public transit ridership varied widely, but the most anyone rides is just two to three days per month. This could be attributed to sunk cost fallacy for car owners or unexamined habits. For interventions, the researchers suggested leveraging defaults and sunken costs with pre-loaded transit cards, gamifying rides with a lottery similar to the one in Durham N.C., and connecting with riders through personalized social-norms text messaging.

And the high frequency “Use it Well” riders take transit four to five days a week and are interested in using it more. The nudges for this group are small, since they already have positive associations with public transit. High frequency users cited “convenience, affordability, not worrying about parking and driving, and the environmentally friendly nature of this mode of transport” as their motivators for taking public transportation. Examples of behavioral interventions include making the ride more social through programs that encourage interaction, like conversation cars, or gamifying incentives to utilize the trains at off-peak times.

Commuter Discounts in Hong Kong

Reducing crowding by nudging users to ride during off-peak hours was the focus of a research paper from the Urban Mobility Lab at the Massachusetts Institute of Technology (MIT). Hong Kong is one of the densest places in the world, with one of the most popular public transit systems on earth; 12 million passenger trips are made on public transport every day.The Mass Transit Railway (MTR) is the main public transit network, but the popularity of MTR has led to traincar overcrowding and station congestion. In addition to railway expansions, the Hong Kong government and transit agency wanted to test behavioral nudges to decrease train usage during peak hours. The researchers from MIT worked with MTR to introduce a morning, pre-peak hour commuting discount fare. Riders had a 25 percent discount if they rode to one of the 29 heavy-use stations before 7:15am (fares on MTR are paid by distance traveled).

Bike commuter

The experiment ran for nine months, and achieved the internal goal of reducing morning peak-hour ridership by 3 percent. There was also a notable reduction in crowding on the morning trains. Researchers did point out that bus service was disrupted for five months during the study, due to protests on the streets of Hong Kong, and that service disruption did increase MTR ridership. However, MTR has adopted the strategy for another year, having found the 3 percent reduction sufficient enough to continue with the discount.

Reducing vehicle transit and encouraging sustainable travel are crucial for cities that want to address everything from public health to pollution to traffic congestion. Knowing that behavioral and social factors influence transit choices, cities have an opportunity to nudge residents toward greener modes of travel. And as the above cases show, simple nudges can result in significant impacts. So perhaps this is a nudge to cities, to encourage them to incorporate behavioral economics into their transit plans.

About the Author

Betsy Gardner

Betsy Gardner is the editor of Data-Smart City Solutions and the producer of the Data-Smart City Pod. Prior to joining the Ash Center, Betsy worked in a variety of roles in higher education, focusing on deconstructing racial and gender inequality through research, writing, and facilitation. She also researched government spending and transparency at the Lincoln Institute of Land Policy. Betsy holds a master’s degree in Urban and Regional Policy from Northeastern University, a bachelor’s degree in Art History from Boston University, and a graduate certificate in Digital Storytelling from the Harvard Extension School.