Sustainable Transportation Through Behavior Change

As the United Nations warned in presenting Sustainable Development Goal 13 on climate action, “To limit global warming to 1.5°C above pre- industrial levels, [greenhouse gas] emissions must already be decreasing and need to be cut by almost half by 2030, just seven years away.” Meeting this goal will require drastic action, particularly in the transportation sector. Transportation is the largest single source of GHG emissions in the US, accounting for 32% of all emissions. Of that 32%, nearly half of emissions are attributable to light duty vehicles.

Recognizing the need for GHG reductions in the transportation sector, California adopted the Advanced Clean Cars II regulation in 2022 that set the ambitious requirement that 100% of new cars and lights trucks sold in California must be “zero-emission vehicles” by 2035. But ample analysis shows that even this rapid transition will not be enough to meet the state’s targets for GHG reductions. For this reason, the state has also set targets for reducing vehicle miles of travel (VMT). VMT reduction is an essential component of the state’s GHG reduction approach and will address many other environmental problems that electric vehicles don’t solve: production and disposal of tires and batteries, wear and tear on pavement, health and safety impacts, susceptibility to weather events, encouragement of urban sprawl, harms to wildlife, and others.

Reducing VMT means getting people to make different choices about their daily travel, including choice of travel mode, the frequency of trips outside of the home, the destinations of those trips, and the routes taken to get there. Reducing VMT to the extent needed from a climate standpoint also requires changes in longer term choices like where to live and whether or not to own one or more cars. Travel behavior researchers study these choices, drawing on psychological as well as economic theory, and their work provides some understanding of how we might change travel behavior so as to reduce VMT and improve sustainability.

First, it must be possible to drive less. The lack of alternatives to driving is a significant barrier to VMT reduction in the U.S., where most communities have been built for cars rather than people. Changing this situation would require a major shift in land use planning to increase residential destinations and reduce distances to destinations such as shops and schools. It would also require a major shift in transportation investments away from projects that expand roads to projects that improve alternatives to driving, including public transit, bicycling, and walking. This shift would make a difference: ample research shows that VMT is significantly higher in car-oriented than more people-oriented communities, even in the U.S.

An important corollary to this first step is that people must see how they can drive less. Changes in land use and transportation planning must be accompanied by programs that help people understand what alternative to driving they have and how they can use them. This means that agencies must provide clear and accessibility information about public transit services and safe bicycling routes. Training programs may also be needed, particularly for segments of the population who would most benefit from using these modes. Examples include transit training for elderly people and bicycle classes for recent immigrants. A program at Google that lent bicycles to its workers and provided support services succeeded in reducing VMT by increasing bicycle commuting. It also encouraged them to try bike commuting.

Second, people must want to drive less. A “carrot” approach to encourage people to drive less is to make it appealing – cool, even. Urban planners can adopt programs from the public health field that use social marketing and physical design to nudge people away from driving. Travel behavior research can help in the design of such programs by pointing to aspects of driving that people don’t like as well as aspects of the alternatives that they do like. Research shows, for example, that “fun” is an important motivation for biking, suggesting that communities can encourage bicycling by leveraging this fun factor through community events and other approaches. The “stick” approach includes both physical restrictions on where cars can go, as is common in many cities outside of the U.S., as well as policies that increase the price of driving. New York City’s recently implemented congestion pricing program immediately led to a reduction in driving within the city.

Third, governments – and the public – must abandon the long-held goal of making driving easier. When public policies make driving easier, for example, by widening highways or providing ample parking, people will naturally drive more. Ample empirical research documents this phenomenon, called “induced travel,” which is explained in simple terms by the economic concepts of supply and demand. In California that evidence has not stopped highway expansion projects that will increase VMT even though the state has official goals for reducing VMT. This paradox raises the question of not just what drivers are thinking but also of what decision makers – and the professionals who work for them – are thinking. Research that illuminates the thinking behind public policy can point to ways to change it.

This recipe for VMT reduction requires a cross-disciplinary effort on the part of researchers. The economic framework that has long dominated travel behavior research would benefit from an applied psychology perspective that delves deeper into the short- and long-term choices of individual travelers as well as the transportation-related policy choices made by public officials. Such research can provide the basis for the design of strategies to improve alternatives to driving, increase awareness and appreciation of these alternatives, and nudge people towards them, away from driving. The trajectory of climate change depends on it.

Sustainable Transportation Through Behavior Change

"The economic framework that has long dominated travel behavior research would benefit from an applied psychology perspective."