NEW YORK CITY—As One World Trade Center surpasses the Empire State Building in height, the project's significance to Lower Manhattan's office sector is indisputable. But it's also helping Downtown become a retail success story.

"The number of commuters and tourists coming through here is staggering," Chase Welles, retail chair at the Real Estate Board of New York, tells Real Estate Forum. "The World Trade Center is the most visited place in New York after the Met in its first year. About 200,000 people a day go through the WTC site, and 300,000 people go through the Fulton Street corridor. Those numbers are just not arguable."

As a result of the growth in tourism, employment and 60,000 new residents, spending in Lower Manhattan is now an estimated at $4.7 billion annually, according to the Alliance for Downtown New York. In turn, 90 new retailers opened in 2011, and at least 13 more are coming soon, the Alliance says.