California PATH

Magnetic Guidance System (MGS)


PATH's Magnetic Marker Reference Sensing and Guidance System was designed by PATH researchers
specifically for vehicle guidance and control. The system can provide very accurate measurements of vehicle
position within a lane, absolute longitudinal location of a vehicle, and advance information about upcoming
roadway characteristics, including roadway curvatures, entrances and exits, mileposts, etc.

System Description:

The magnetic guidance system comprises a series of magnetic markers that serve as a roadway reference, plus
vehicle-borne sensing and processing units that obtain information from the markers. Simple permanent magnets
embedded in the center of a lane, about 1.2 meters apart, indicate the lane center. Alternating the magnetic
polarities of the markers (north-up vs. south-up) creates a binary code that indicates roadway characteristics.
One binary-coded message about roadway characteristics requires an average of 25 markers, which takes up
30 meter's length of roadway. The elapsed time to read that message would be about a second for a vehicle
traveling at 100 km/h (60 mph).

Fluxgate magnetic sensors, mounted under the front and rear bumpers of a vehicle, measure the magnetic fields
on three axes. A Pentium computer in the trunk processes the magnetic field data to derive lateral and longitudi-
nal position measurements and to decode the binary information. (The computer also performs all other vehicle
control functions.)


Over the past 10 years of extensive tests and evaluation, the PATH magnetic guidance system has demonstrated
excellent performance:

  • Lateral position accuracy of 5 mm (root mean square) 
  • Longitudinal position accuracy of 5 cm (root mean square) 
  • Highly robust and reliable under realistic environmental conditions 
  • Fail-safe. 

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Cost Example - Interstate 15,
San Diego, California

8 Car Platoon under Computer Control
(Eighth car undergoing automatic lane change)

Magnetic markers were installed on two lanes of an eight-mile length of High Occupancy Vehicle (HOV) lanes
for Demo '97 in San Diego. Most markers are ceramic magnets (2.4 cm diameter, 10 cm long, 9 each), with
neodymium magnets (2.5 cm diameter, 2.5 cm high, less than $10 each) used for special locations where rebar
is close to the surface. The cost per lane mile of installation was less than $10,000. When the installation process
is automated, this cost can be substantially reduced.
Why Magnetic Markers?

The PATH guidance system has been tested and proven to be robust under a wide variety of operating
conditions. Falling or accumulated rain or snow does not affect it. It provides extremely accurate and repeatable
measurements. The system is able to detect failures of roadway markers and of vehicle-borne sensors. The
infrastructure cost is low, with usable life exceeding pavement life and no maintenance required. The combination
of absolute position information with the system's coded preview of roadway characteristics offers added
functionalities and performance for vehicle guidance and control.

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Hands Free Driving 
1.7Kb Quicktime Movie


The PATH magnetic guidance system can be used for a variety of vehicle 
guidance and control applications, including:

  • Automatic steering control reference for all vehicle classes 
  • Lane departure warning reference for all vehicle classes 
  • Precision docking reference for transit buses 
  • Guidance reference for snowplows 
  • Special applications in difficult environments (maintenance yards and shops, tunnels, mines, terminals, ports) 
  • Automated Vehicle Location (AVL) for fixed route operations
For further information

PATH is interested in developing additional applications for this technology, and in customizing it for such applications.
We are also seeking partners for commercialization of the technology in transportation and other related fields of activity. Please contact Wei-Bin Zhang or Steven Shladover at 
(510) 231-9495 for technical information and Douglas Crawford at (510) 643-4218 for technology licensing.

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High Performance Lateral Control


(Click for Larger View Showing Accuracy of Magnetometers)


Fully Automated Control for Heavy Duty Vehicles


3 Axis Fluxgate Magnetometer & Ceramic Magnet


Advanced Guidance & Control for Hwy. Snow Removal


Workers installing Magnets in Road Surface


Transit Bus Precision Docking and Guidance

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PATH Home | This Pages by PATH Design Team | April 1998