Our world is becoming increasingly urban. In 1990, there were 10 mega-cities with populations of 10 million or more. By 2014, there were 28 mega-cities. By 2030, the UN projects we'll have 41 cities with more than 10 million people each. As more people head for the bright lights of the big city, how can we fight back against pollution and traffic congestion?
One of the world's most beautiful cities has an ambitious plan to reclaim their space. Barcelona is launching a program called superblocks ("superilles" in Catalan). It carves out nine-square-block mini-villages where cars aren't very welcome.