Richard Thaler and Cass Sunstein’s “nudge theory” defines a nudge as “any aspect of choice architecture that alters people’s behavior in a predictable way without forbidding any options or significantly changing their economic incentives.” Transportation agencies across the United States have applied nudge theory to public policy, specifically in regards to transit.
In 2018, 28% of all energy used in the US was to power transportation, and over half of that can be attributed to gasoline. Further, light-duty vehicles were responsible for almost 60% of US transportation sector greenhouse gas emissions in 2017. As public awareness of the danger of burning fossil fuels grows and climate change becomes a topic of national discussion, transportation agencies have turned to nudge theory to change traveler behavior.
Transit incentive programs offer rewards in an attempt to nudge travelers toward a transit agency’s preferred behavior pattern. The goal of these programs is typically to reduce congestion, emissions, or energy use, or to improve air quality. Administrators generally design programs to change one of three trip elements: mode, time, or route of travel.
- Mode nudges aim to encourage passengers to use a different form of transit, often focusing on shifting travelers from single-occupant vehicles onto public transportation or bikes.
- Time nudges seek to shift the time of day during which a passenger is traveling, usually encouraging passengers to commute at nontraditional hours.
- Route nudges attempt to divert passengers away from congested areas and are the least commonly used of the three incentive types.
These nudges seek to reduce traffic congestion, which directly impacts emissions. Congestion on roads results in increased vehicle idling, which the US Department of Energy estimates generates 30 million tons of carbon dioxide each year. Eliminating personal vehicle idling would have the same impact as taking 5 million vehicles off the roads.
A Washington, DC and Baltimore program launched in 2019 is one example of a mode nudge intended to get cars off the road. Developed by the DC-area government program Commuter Connections, the Incentrip program offers cash and gift card rewards for environmentally responsible and congestion-reducing modes of travel. Incentrip operates on a points system, with more points awarded for walking, biking, public transit, and carpooling than for driving a single-occupant vehicle. If users travel by car, the app provides points for “eco-friendly” driving by analyzing braking and acceleration patterns and distributes more points during peak commute hours than during other times of the day, in a further effort to reduce congestion. Travelers can redeem points for cash and gift cards once they reach various thresholds.
Lei Zhang, head of the Maryland Transportation Institute at the University of Maryland, which developed the Incentrip app for Commuter Connections, reports that the program has indeed “nudged” some users to change their behavior. At one point during the program’s pilot phase, it reduced peak period traffic by 27%.
However, Incentrip faces challenges. The app interface is not intuitive and the points structure is complex. Travelers generally must alert the app before beginning a trip—which may discourage potential users from making Incentrip part of their daily routine. Finally, the app makes little distinction between biking, walking, public transit, and ridesharing, despite the outsized impact of biking and walking on emissions reduction. A 2011 report from the European Cyclists Federation compares bicycle emissions—from bicycle production materials and cyclist diets—to other transportation mode emissions. Predictably, the report finds that bicycle emissions are over 10 times lower than those stemming from single-occupant vehicles. However, it also finds that bicycle emissions are almost five times lower than bus emissions.
Incentrip provides some elements of gamification—a points system, weekly challenges, and the opportunity to “level up”—but Stanford University’s Congestion and Parking Relief Incentives (CAPRI) study went a step further. The CAPRI study imposed a time nudge by incentivizing drivers to commute during off-peak hours in order to reduce congestion around the university. Points earned for desirable commute behavior could be traded for a set cash value or used to play a chutes and ladders-style game with random cash prize results.
Because the CAPRI study operated on a small scale, it was able to offer more creative and flexible rewards such as tickets to high-profile sporting events to incentivize behavior shifts and encourage enrollment. Similarly to Incentrip, however, the CAPRI study did not award preference to walkers and bikers, missing an initial opportunity to encourage the most effective congestion- and emissions-reducing forms of travel. Despite this, the CAPRI study has been considered successful. Though it ended in 2014, it led to the university creating its “Commute Club,” offering incentives like carpool and Zipcar credits, cash, and opportunities to win prizes in drawings for members who exhibited desired behaviors.
Incentrip and the CAPRI study are only two of many programs that agencies have used to explore how incentives may modify transit decisions. Other active transit incentive programs in the US include Go Santa Cruz in Santa Cruz, CA, CommuteRewards in Charlotte, NC, and CTrides in Connecticut. As transportation technology becomes increasingly sophisticated, urban areas more crowded, and climate change more politically salient, we will likely see more of these programs launch. While no federal programs have been proposed, the anticipated introduction of autonomous vehicles has the potential to send shock waves through the transportation policy space. How the federal government addresses autonomous vehicles may signal whether transportation incentives could be scaled to minimize congestion and emissions across the nation.
To learn more about the environmental impact of emissions from car, plane, bus, rail, and boat transportation and key legislation, download National Journal’s Impact of transportation on energy and the environment deck.