Megacities

How do the world's major cities keep functioning? While planes usually require a two-minute gap between departures, at Heathrow, the world's busiest airspace, this margin has been reduced to 45 seconds. Watch how air traffic controllers manage this unique and highly regimented flight pattern. Also see how traffic on the streets and on the Thames is regulated.

In a city where 75 percent of the people don't have a car, the New York subway offers the best transit system in America. Follow the emergency management response team as they plot rescues, escapes and re-routing on the system, in order to ensure the safety of both the riders and workers of the subway. The threats range from breakdowns to flooding to terrorism.

Hong Kong is one of the most densely populated urban regions on the planet. In the recent past it has been rocked by economic and financial upheaval. It now has the most high-tech, counterfeit-proof currency in the world, as well as some of the most complex bank building structures. An immense technological feat.

Constructed in the nineteenth century, the sewers of Paris extend 2300 kilometres - the distance from Paris to Istanbul. Follow Phillipe Bussignies and his team as they lay out thousands of miles of fibre-optic cables through the sewer tunnels using a Cable Laying Robot. Paris plans to become the world's first fully-connected wireless city.

Public transportation is Mumbai's lifeline. The trains were built for 1700 passengers, but in this mega city, they carry three times that number. And the crowding will only get worse. Look at Mumbai's large scale lunch delivery known as the dabbahwallah system, which is recognised as one of the best managed supply chains in the world. Forbes magazine awarded the system its highest rating.

To Mother Nature, Mexico City is one big target. On one side: one of the world's most earthquake-prone hotspots. On the other: one of the world's most active volcanoes. And beneath their feet - a shaky foundation of landfill. From subways to freeways, this episode examines how Mexico City is harnessing cutting-edge technology to build in safety.

More than 10 million people live in Sao Paulo and every day, they generate 14,000 tons of garbage. But Sao Paulo is undergoing a green revolution. Follow one aluminum can from the time it is picked up by one of the catadores (trash-pickers, who make their living from collecting recyclables) through pressing, melting, and re-melting, to the moment it is ready to become a new can.

What keeps this gambling city aglitter? The Las Vegas power grid is a network of six power plants fuelled by nearly every source of energy: hydro-electric, coal and natural gas. From Harley-riding linemen to the no-nonsense, tell-it-like-it-is Mayor Oscar Goodman... and from livewire helicopter workers to a quirky couple living 'off-the-grid', see how Las Vegas maintains its sparkle.

Half a kilometre high, Taipei 101 is the tallest skyscraper on the planet, towering over one of the world's busiest cities. The ultimate in design and engineering, it is a statement of power and prestige. Yet it hovers over Taiwan's capital, Taipei, a city that sits within the "Ring of Fire", the most seismically active area on Earth. Will its shape, inspired by nature, and futuristic design prevent this modern symbol of a new Taipei from being toppled by the elements?