Vehicle Lateral Warning, Guidance and Control Based on Magnetic Markers: PATH Report of AHSRA Smart Cruise 21 Proving Tests

Problem

PATH tested a vehicle that provides automatic steering control, driver lane guidance control, and lane departure warning at the test track of PWRI in Tsukuba City, Japan for the "Smart Cruise 21" proving tests. The steering warning/guidance/control system developed by PATH includes magnetic sensors to detect the vehicle lateral deviation relative to the magnetic markers installed on the roadway; an antenna to receive the radio-wave control point marker information; an automatic steering actuator; a display screen showing the anticipated position of the vehicle to support the driver in steering the vehicle; and a speaker to provide an audio warning signal to the driver when the car is off-course. This system addresses prevention of overshooting on a curve, support for prevention of lane departure under expressway speed condition, and support for prevention of lane departure under fog and rain condition. Only the issues related to steering control are addressed; throttle and brake are controlled by the driver.

This report focuses on the discussions of the following five proving test items that are related to the magnetic markers sensing system:

1. Capabilities of the PATH steering warning/guidance/control system based on the benchmark test results to support the prevention of overshooting on curve, prevention of lane departure under expressway speed condition, and prevention of lane departure under fog condition.
2. Results from the PATH Demo2000 scenarios to further substantiate the steering effectiveness of the magnetic marker based lateral warning/guidance/control system.
3. Presentation of the proving test results of the PATH steering warning/guidance/control system without the knowledge of the road curvature information.
4. Comparisons of the performance of the PATH steering warning/guidance/control system with respect to 2m, 4m, and 6m magnetic marker spacing.
5. Discussions on the effects of different magnetic markers (nail and plate types) on the PATH and AHSRA magnetic sensing system, as well as on noise characteristics observed on the North Loop of the test track.

Findings

1. The capability of the steering warning/guidance/control system based primarily on the magnetic markers was shown to be effective to support automated steering control, driver steering control based on the display screen information alone, and driver steering control based on lane departure warnings alone.
2. The results from the PATH Demo 2000 scenario proved to be very successful. No failures occurred during four days of demonstration and five days of rehearsal. The Demo 2000 scenario included automated steering around the entire test track at various speeds and road curvatures, obstacle detection, switching between manual and automated steering, and steering guidance in zero visibility conditions.
3. The dynamic performance of the PATH guidance/control/warning system is very similar with or without the knowledge of road curvature.
4. Satisfactory performance for the proving test can be obtained using 2-meter magnetic marker spacing. The performance degradation from 2m spacing to 4m spacing is relatively small except at very low speed or sharp curves. Noticeable performance degradation can be observed from 4m to 6m marker spacing especially at lower vehicle speeds. High speed on a straight curve is the least sensitive to the increase of the marker spacing, except at very large departure angles. Low speed on sharp curves is the most sensitive to an increase in marker spacing.
5. a) A "noisy section" exists on the North Loop of the test track. The earth field "noises" in the "noisy section" are observed to be greater than those from the normal section. b) The results do not show a clear distinction between the nail and plate type magnets. However, this may not be true for the AHSRA sensors when the vehicle height is changing. c) AHSRA sensor measurement is not smooth when the magnet is directly between two sensors-this was the reason PATH used only the PATH magnetic sensors for the proving tests.