And why we may soon not be able to measure it at all.
Europe's airplane activity in this visualization looks like a hive of angry, electrified bees.
The Perfect Commute
The next-generation fare card will definitely be much more than a fare card. But what, exactly?
A 27-year-old woman was left as a newborn in restaurant bathroom, but now is tracking down her biological mom on Facebook.
Wendy MacNaughton cuts through the noise with Meanwhile in San Francisco: The City in its Own Words.
One More Thing
A dramatic art installation in Adelaide, Australia.
2013 saw 10.7 billion passenger trips, the highest in almost 60 years.
The fear of cancer from radiation exposure has led to a new set of problems for young families.