RFID tags in the road hold promise for smarter vehicle location systems

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.

Many vehicle location and positioning applications are built around Global Positioning System (GPS) technology, which, in theory, provides the capability to locate a GPS-equipped vehicle anywhere on the Earth’s surface. However, in practice, GPS is limited by the need for clear ‘views’ of orbiting satellites; bridges, tunnels, and the urban canyons of downtown areas can block or interfere with GPS signals, resulting in unacceptable gaps in service.

The technique developed by a University of Minnesota team promises to help fill many of these gaps, augmenting GPS with a means of determining location that is not affected by the types of interference that plague satellite-based technologies.

Coded RFID (radio frequency identification) tags embedded directly in the roadway can be activated and read by sensors mounted on a vehicle, in the same way that sensors in the doors of shops activate and read RFID anti-theft tags. Because each tag in the road is programmed to read out the lane in which it is located and its linear distance along the road from a landmark point, the vehicle’s onboard navigation system can find out exactly where it is every time it passes over a tag.

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 bus navigating urban freeways, many obstacles can interfere with the GPS signal— forcing the receiver to spend crucial seconds re-acquiring the satellites in order to compute a new position.

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 a research project by the University of Minnesota a vehicle positioning system (VPS), used RFID tags embedded at regular intervals along the centre of highway lanes. A tag reader antenna mounted along the front bumper of a vehicle activates the tag as it passes, retrieving the encoded data and passing it to an onboard computer.

Several 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, combining RFID positioning with inter-vehicle communication using Digital Short-Range Communications (DSRC).

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.

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.

Source: ITS Sensor, Intelligent Transportation Systems Institute at the University of Minnesota, Minneapolis, Minnesota.

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