Carnegie Mellon University

Traffic in an intersection

October 23, 2018

How vehicle-to-vehicle communication could replace traffic lights and shorten commutes.

By Ozan Tonguz

Krista Burns

The following article appeared in the October 2018 IEEE Spectrum print issue as “Red Light Green Light—No Light.” The Carnegie Mellon startup startup, Virtual Traffic Lights, LLC, is the cover story of the October issue of IEEE Spectrum Magazine, the flagship publication of IEEE that goes to 400,000 IEEE members all over the world.

Photo credit: Dan Saelinger

Life is short, and it seems shorter still when you’re in a traffic jam. Or sitting at a red light when there’s no cross traffic at all.

In Mexico City, São Paolo, Rome, Moscow, Beijing, Cairo, and Nairobi, the morning commute can, for many exurbanites, exceed 2 hours. Include the evening commute and it is not unusual to spend 3 or 4 hours on the road every day.

Now suppose we could develop a system that would reduce a two-way daily commute time by a third, say, from 3 to 2 hours a day. That’s enough to save 22 hours a month, which over a 35-year career comes to more than 3 years.

Take heart, beleaguered commuters, because such a system has already been designed, based on several emerging technologies. One of them is the wireless linking of vehicles. It’s often called vehicle-to-vehicle (V2V) technology, although this linking can also include road signals and other infrastructure. Another emerging technology is that of the autonomous vehicle, which by its nature should minimize commuting time (while making that time more productive into the bargain). Then there’s the Internet of Things, which promises to connect not merely the world’s 7 billion people but also another 30 billion sensors and gadgets.

All of these technologies can be made to work together with an algorithm my colleagues and I have developed at Carnegie Mellon University, in Pittsburgh. The algorithm allows cars to collaborate, using their onboard communications capabilities, to keep traffic flowing smoothly and safely without the use of any traffic lights whatsoever. We’ve spun the project out as a company, called Virtual Traffic Lights (VTL), and we’ve tested it extensively in simulations and, since May 2017, in a private project on roads near the Carnegie Mellon campus. In July, we demonstrated VTL technology in public for the first time, in Saudi Arabia, before an audience of about 100 scientists, government officials, and representatives of private companies.

The results of that trial confirmed what we had already strongly suspected: It is time to ditch the traffic light. We have nothing to lose except countless hours sitting in our cars while going nowhere.

The principle behind the traffic light has hardly changed since the device was invented in 1912 and deployed in Salt Lake City, and two years later, in Cleveland. It works on a timer-based approach, which is why you sometimes find yourself sitting behind a red light at an intersection when there are no other cars in sight. The timing can be adjusted to match traffic patterns at different points in the commuting cycle, but that is about all the fine-tuning you can do, and it’s not much. As a result, a lot of people waste a lot of time. Every day.

Instead, imagine a number of cars approaching an intersection and communicating among themselves with V2V technology. Together they vote, as it were, and then elect one vehicle to serve as the leader for a certain period, during which it decides which direction is to be yielded the right-of-way—the equivalent of a green light—and which direction has the red light.