The whirlpool of induced demand

Each of our transportation choices, no matter how small, have far-reaching effects. Every day, people make the decision to drive, take transit, bike or walk. And every day, some people move to a new home, and choose the location of that home based on the transportation choices available to them.

When we reconfigure an intersection to become more walkable, we push the balance toward walkability. When we add freeway ramps or parking lots, we push the balance toward driving. And these decisions feed upon themselves in a cycle.

The more appealing walking is, the more likely people will choose places to live based on walking, which creates political pressure to make streets safer and more appealing to walk. The easier driving is, the more people will live great distances from work, creating more traffic and pressure for more roads which make walking impossible.

This cycle has its own inertia, like water moving in a whirlpool. The faster we move in one direction, the harder it is to move the other way. Some cities, like San Francisco, are circling in a more transit-friendly direction. Others, like Atlanta, are still circling the other way, though slower. DC is like turbulent water, not moving one way or the other. Some days, we push a little bit one way, by traffic calming an intersection or turning a superblock into a regular street grid. Other days, we push the other way, widening a freeway bridge or turning a bit more park into parking.

I care about, and harp on, the little things because each small push in the car-centric direction speeds up the whirlpool that way, and the decisions we make will last for decades. DC was moving rapidly in the direction of more freeways and more traffic until activists blocked many of the freeways and Presidents Kennedy and Johnson make Metro possible and saved DC as a walkable city. Without vigilance, we may gradually start circling the drain once again.