The morning I wrote this I took public transportation to work. I hopped on the bus around the corner from my house, then the train for a few stops farther. I took mass transit because it was convenient, because my card was already preloaded with the cash that diverts from my paycheck, and because the ride gave me 20 minutes to start the day browsing Twitter.

Baked into this decision, however, were a number of other nearly subliminal calculations about the alternatives not taken. I did not drive the car (yes, my household has a car) because downtown Washington, D.C., is a hot mess at rush hour, and because parking near the office costs the equivalent of a fancy hamburger a day. I did not bike because it was snowing. (Again.) And I did not walk because the distance was too far.

My commuting choices—just like everyone’s—are the sum of the advantages of one transportation mode weighed against the downsides of all other options. Or, more succinctly: my feelings about the bus are mediated by what I’m thinking about my car.

At a macro level, this decision-process implies that there are two ways to shift more commuters out of single-occupancy vehicles and into other modes of transportation, whether that’s biking, carpooling, walking, or transit. We can incentivize transit by making all of those other options more attractive. Or we can disincentivize driving by making it less so. What’s become increasingly apparent in the United States is that we’ll only get so far playing to the first strategy without incorporating the second.

“One of the things I keep looking at is cities like Boulder, Davis [California], and Portland—places well-known for walking and biking,” says Daniel Piatkowski, a recent graduate of the design and planning doctoral program at the University of Colorado at Denver. I met him in 2014 at the Transportation Research Board annual conference, where he was presenting on what he’s simply come to describe as the “carrots” and “sticks” that might be deployed to get people out of their cars.