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Center for Transportation Studies

Programs & Labs

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Spring 2007

“Tags” in the road hold promise for smarter vehicle location systems

Photo of RFID Car

A probe vehicle was used to test potential transportation-related applications of RFID tags. A tag “target” is in the foreground—in use, tags would be much smaller.

What makes intelligent vehicles smart? The ability of a vehicle to “know” where it is at any given moment is one measure of intelligence that enables a host of intelligent transportation systems applications, from basic navigation assistance to automatic collision warning.

Today, the Global Positioning System, a network of satellites broadcasting navigation signals from fixed points in space, is the backbone of many systems that require constant navigational information. University of Minnesota researchers have developed several advanced driver-assistive systems using GPS technology. But by its very nature, GPS suffers from limitations that keep it from being the ideal single solution to the location needs of intelligent vehicles.

Intelligent Vehicles Laboratory director Craig Shankwitz and graduate student Matthew Bevilacqua are among the researchers developing new technologies that will augment GPS, in order to meet the need for more robust location information in tomorrow’s intelligent vehicles. Recently the researchers have examined the potential use of a technology commonly seen outside of transportation—RFID, or radio frequency identification.

Most people today are familiar with RFID through the use of small RFID tags as theft-deterrent devices that must be removed or deactivated before leaving a store. But the technology actually has a long history in transportation: as early as 1973, a prototype system was developed with possible applications including automatic vehicle identification and toll collection.

A passive RFID system works by encoding information on small, unpowered electronic circuits that can be embedded in tags or capsules. When these circuits are close to a specially designed radio transmitter, the power from the transmitter produces a signal from the RFID circuit; these signals can transmit a small amount of unique information that has been encoded within them, such as an identification code.

Why use RFID at all? Using satellites gives GPS great advantages, like the ability to cover the entire surface of the planet. But in order to determine a position accurately, GPS receivers require direct line-of-sight signal paths to at least three GPS satellites at all times. For a ship cruising on the open ocean, this is usually no problem, but for a bus navigating urban freeways, many obstacles can interfere with the GPS signal—even passing under a bridge can disrupt the signal, forcing the receiver to spend crucial seconds re-acquiring the satellites in order to compute a new position. Other factors, such as confusing signal reflections from the sides of tall buildings in “urban canyons,” also impede the effectiveness of GPS.

For some applications, such as guiding a driver along a route to a destination, the minor disruptions caused by signal loss may be tolerable. But for other safety-critical tasks such as helping a bus driver operate on narrow road shoulders or collision avoidance on congested urban roads, temporary signal loss can spell disaster.

In the IV Lab’s vehicle positioning system (VPS), RFID tags would be embedded at regular intervals along the center of highway lanes. A tag reader antenna mounted along the front bumper of a vehicle would activate the tag as it passes, retrieving the encoded data and passing it to an onboard computer.

The positional information provided by the RFID system is very different from that provided by GPS—instead of coordinates on the surface of the Earth, it shows a vehicle’s position as a distance along a roadway. This is actually not a disadvantage, because lane position and linear distance on a road is precisely the information required by many ITS applications. In order to get this information, GPS coordinates must be matched against high-accuracy digital maps of the road network, requiring more computation and introducing additional possibilities for error.

But the greatest promise of this new system may not be as a replacement for GPS, but rather as a complementary technology. VPS could provide high-accuracy positioning in areas where GPS cannot achieve the required accuracy.

To demonstrate the possible use of RFID-based positioning, the IV Lab researchers implemented a basic collision-avoidance system using the technology.

Several academic and industry groups are currently researching “electronic brake light” systems that warn drivers when they are in danger of striking a leading vehicle that has suddenly slowed down. The IV Lab system combines RFID positioning with inter-vehicle communication using the emerging Digital Short-Range Communications (DSRC) standard now under development by a consortium of vehicle manufacturers, researchers, and federal transportation agencies.

In the experimental system, a lead vehicle was equipped with an inertial sensor that registered any sudden deceleration. An onboard DSRC unit then transmitted a braking warning, which would be received by all vehicles in the immediate area, along with the position of the braking vehicle. Because the warning would only be useful to a vehicle following close behind the lead vehicle, the following vehicle in this experiment was equipped with a computer system that compared the location of the braking vehicle with its own location, and activated a warning buzzer if it determined that the two vehicles were close enough to create a dangerous situation.

The researchers note that the experimental electronic brake light system developed during their research is intended to demonstrate a potential application of VPS technology—not to serve as a real-world safety system. Following successful tests of the experimental system, the research team continued to explore ways to make the system more robust. By incorporating additional information from onboard sensors and using more advanced computational techniques, they developed a second generation approach to identifying potential crash risks for platoons of moving vehicles.

Findings from the experimental electronic brake light system are now being applied to the development of a system to assist bus drivers in maintaining position in a narrow shoulder lane when GPS signals are unavailable.

Although the development of RFID-based vehicle positioning systems offers great potential to enhance current positioning technologies, the researchers note that today’s commercial RFID systems may not be adequate for the development of robust solutions. Custom transportation-focused RFID systems could be developed to meet this need; however, the rapid advance of RFID technology may soon make RFID a viable tool for ITS applications.