London

Reuters/Tony Melville

One Downside to Bicycle Commuting: Biker's Lung

London bike commuters found to breathe in more soot than pedestrians

2010 File photo Associated Press/The Philadelphia Inquirer

Are Violent 'Flash Mobs' Really a Trend?

After two summers in a row of disturbing group violence in cities like Chicago and Philadelphia, authorities look at the intersection of technology, poverty, and race

Yuriko Nakao, Reuters

The 25 Most Economically Powerful Cities in the World

Most of the world's capacity for economic growth is centered in its metro areas. Which cities top the list?