Transportation researchers have long suspected it to be true that you’ll only spend so much time commuting. You have a travel-time budget in your head – for most of us, it’s about an hour a day – and you’ll only commute as far as you can get in that time, given your mode of travel. Maybe you can train across town and back in an hour, or drive 20 miles in from the suburbs and home again in that time, or walk a mile-and-a-half to the office and back. The distances may vary, thanks to technology, but the "time budget" remains roughly the same. This thesis – called Marchetti's Constant – theoretically holds true going all the way back to the cave man who had to drag his knuckles with him.
"If technology allows you to go farther away, to go faster, you will go farther away," says Carlo Ratti, the director of the Senseable City Lab at MIT. "But the budget in terms of time is always the same. It was the same 2,000 years ago, it is the same today."
But how would you prove that some patterns of human mobility are universal across location, or culture, or even time period? Traditional measures for tracking commuter behavior certainly aren't constant across the world. Researchers now have some novel tools for studying commuting patterns, some of the most interesting of which revolve around cell phone data. But it's usually only possible to look at communications traffic from a single city, or one country, based on a data-sharing arrangement with a single telecom carrier.
"Wouldn’t it be very interesting to start comparing this type of data from many different cities?" Ratti asks. "Comparing, say, what happens in New York, and London, and Hong Kong, looking at, 'how do different cities behave?'" Or, rather, how do we all behave the same?
A few months ago, the Senseable City Lab worked out a deal to gather exactly this sort of global information not from telecom carriers directly (those companies differ country to country), but from Ericsson, the Swedish provider of telecommunications equipment to much of the world. The data they’ve gathered is aggregated at the antenna level, allowing researchers to parse patterns in how we move and relate to each other at the local and global scales through our voice, SMS and data traffic.
"That's why we started calling the [research project] the Signature of Humanity," Ratti says, "because it's about some common things that happen everywhere, but also some very local signatures and very local features that we are discovering."
With their initial cache of worldwide telecom data, the lab put together this mesmerizing animation of a "journey into the cellphone network":
The lab is planning next to deeply compare New York, London, and Hong Kong, with the project widening from there.
"If you look down the line," Ratti says, "what we really want to try to do is try to look at mobility patterns of people, for instance across many countries and many cities, to see how people move, how much time people spend moving and commuting every day in cities across the world."