Cell Phone Traffic

Cell Phone Traffic Photo Credit: Clipart.com

Many people stuck in traffic pass the time or take care of business by making calls on their cell phone. Now, scientists have found another way to put that talk time to work. You'll hear about it in this Science Update.


Talking about traffic. I'm Bob Hirshon and this is Science Update.

Bad traffic's no longer a problem relegated to major metropolitan areas. Even commuters in smaller cities now face long traffic delays. Unfortunately, the complicated technology used by big cities to monitor traffic flow is expensive, putting it out of the reach of most local governments.

But Bill Knee of the National Transportation Research Center at Oak Ridge National Lab believes that the ubiquitous cell phone can change that. He and his colleagues are testing a system that uses cell phone signals to monitor traffic flow.


A phone has to self-orient itself occasionally with, with cell towers. And so, with that information, in seeing how a phone travels through a particular zone, and averaging a large number of these phones, you can pretty much get an estimate of travel time.

That information's fed into a computer, where it's processed to interpret how traffic's moving on major roads.

The complete system includes improved traffic cameras and will be tested in Knoxville over the next year. Knee says the system should spot accidents and predict traffic jams in stretches of road as short as a quarter of a mile. For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

When an airplane flies across the country, the pilot is always in touch with the nearest air-traffic control station on the ground. As the plane travels, it gets handed off from one control station to the next. For example, traveling south along the East Coast, you’d say goodbye to New York and hello to Philadelphia, then to Baltimore, DC, and so on.

Cell phones work in a similar way. Unlike land lines, which rely on interconnecting cables to carry their signals, cell phones use radio signals that are received and transmitted through communication towers. These towers are peppered across the country, and each tower services a small zone called a cell (get it). A typical cell is 10 square miles, but they can be smaller or bigger depending on the population of an area.

Just like an airplane passes from one air traffic control tower to another, a cell phone is handed off from one communication tower to the next as it moves through a city's cells. You may have noticed this happening if you have carried a cell phone with you in a car, or on a train or a bus. As you pass from one cell to the next, sometimes the phone has to take a second to find the new signal, so it will go out of service for a second or two and then beep back on.

Knee's system takes advantage of this process by using it to track traffic. Since cell phones each have unique identifiers, it's possible to track the movement of a particular cell phone as it travels around a city. If that cell phone happens to be in a car, you can use that information to figure out how fast the car is moving. And if you can keep track of thousands of cell phones at once, you can use that information to identify traffic jams on the city's major arteries. Knee says that may even help local police identify possible accidents: if traffic seems to be flowing fine in a particular spot and then suddenly stops, there's a good chance that an accident has happened.

In order for this system to work, the cell phones don't have to be in use—they just have to be turned on. And you can do all of these things without knowing exactly who each cell phone belongs to, or eavesdropping on people's conversations.

This system demonstrates the power of piggybacking onto existing technologies to accomplish a new task. There are many other examples. Receivers for the Global Positioning System, a worldwide network of navigation satellites originally built for the military, are now found in cars, laptops, and all kinds of consumer electronics. Several organizations are taking advantage of the down time on people's personal computers by offering free screensavers that process scientific data. And the Internet itself is really an expansion of a military computer network that dates back to the late 1960's.

Now try and answer these questions:

  1. What does the "cell" in "cell phone" refer to?
  2. How does this system use cell phones to track traffic patterns?
  3. Why use cell phones? Why not just build a new system?
  4. Why is it important to study traffic patterns? What kind of knowledge can be gained from this system?
  5. Suppose the police knew the cell phone number of a suspected bank robber. How could this system be used to catch the robber? What are its limitations?

For Educators

The National Transportation Research Center, which Knee directs, examines the safety, environmental impact, energy efficiency, and effectiveness of the nation's transportation systems.

How Cell Phones Work, by How Stuff Works, gives a detailed explanation of the technology behind wireless voice communication.

The Global Positioning System (GPS) is another satellite technology that many modern inventions take advantage of. Learn about it in this primer from the Aerospace Corporation.

Screensaver Lifesaver and SETI at Home are two popular screensaver programs that use unused computing time to do scientific research (in search of potential cancer cures and signs of extraterrestrial life, respectively).

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