In the six years that Janette Sadik-Khan has headed the New York City Department of Transportation, streets have been transformed. Across the five boroughs, 26 acres of asphalt were converted into 50 pedestrian plazas. New bus lanes are speeding transit trips on major thoroughfares in Manhattan, the Bronx, Staten Island, and soon Brooklyn. The city added dozens of miles of protected on-street bike lanes — groundbreaking designs for an American city — and 350 miles of bikeways overall. The biggest bike-share system in the country launched this May, and now regularly sees 40,000 trips per day.

So what is the lesson from this new era of change on New York City’s streets?

“You can remake your streets, quickly, inexpensively — they can provide immediate benefits and it can be quite popular,” says Sadik-Khan in her TED talk.

These changes have improved safety, boosted retail performance, and elicited impressive public approval ratings despite TV and tabloid coverage that tended to be outlandishly negative. Sadik-Khan emphasized that it wouldn’t have been possible to accomplish so much in such a short time frame if it weren’t for the original stroke of genius: the decision to test things out to see what succeeds.

“The temporary materials are important because we were able to show how it worked,” she says. “I work for a data-driven mayor, as you know, so it was all about the data. If it worked better for traffic, if it was better for mobility, better for business, we would keep it. And if it didn’t work, no harm, no foul, we could put it back the way that it was because these were temporary materials, and that was a very big part of the buy-in.”