Randy Cohen, who writes "The Ethicist" column for The New York Times Magazine, says:

In New York at 33rd and Broadway, it's a big transportation hub. Penn Station's right there. A lot of commuter trains stop there, a major subway stop. Thousands and thousands of people pouring out…and what everybody wants more than anything else is: They want a taxi.

And the most appalling episodes of violence I've seen since I've been here—and I've been in New York for 30 years—were committed there. People did just terrible things.

Then about 10 years ago, someone—I guess, the Taxi and Limousine Commission—they did something very simple. They painted a yellow strip down the sidewalk and they stenciled two words on the sidewalk: Cab Line. It utterly transformed behavior there. It's the most astonishing thing. Nearly everyone, almost all the time, simply waits in line. It's magnificent. It's never enforced—there are no "line" police there. But we changed the physical conditions and made it possible for people to behave, invited them to behave, and they do!