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London Olympic StadiumWhen the torch is lit Friday and the 2012 Olympics in London get underway, seven years and some $20 billion worth of preparations will end. But what will happen to the city's Olympic venues once the games are over? A look at former host cities suggests the facilities could face an uncertain future.London plans for its Olympic venues to be repurposed. The publicly owned, 80,000-seat Olympic Stadium (pictured), for example, has a temporary upper tier that can be dismantled after the Games to create a 25,000-seat venue better suited to everyday events.And the Olympic Park, situated in a formerly run-down East London industrial zone, is slated to become an urban ecological oasis and a hub for the new East London Tech City development. Athlete villages will be turned into affordable housing, and other sporting facilities will be made available to clubs, universities, and the public. (See pictures of East London in National Geographic magazine.)But repurposing schemes have been touted at past Olympics, with varying degrees of success."It's unclear if [London is] going to be successful," said Smith College economist Andrew Zimbalist, author of the International Handbook on the Economics of Mega Sporting Events."If you really want to develop a part of a city like East London, it probably makes sense not to use 250 acres [100 hectares] and hundreds of millions of dollars on an Olympic park and stadium. There are probably better uses for that money," Zimbalist said.—Brian Handwerk

Photograph from Yomiuri Shimbun/AP