Vehicle Lateral Warning, Guidance, and Control Based on Magnetic Markers
at AHSRA Smart Cruise 21 Proving Tests

Han-Shue Tan, Benedicte Bougler

During the period of October 6 to December 1, 2000, PATH engineers performed proving tests on the test track of the Public Works Research Institute (PWRI) of the Ministry of Construction in Tsukuba City, Japan. The discussions below of the following five proving test items are related to the magnetic marker sensing system. The depth of the discussions reflects the amount of data available from the proving tests.

(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 Demo 2000 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 the different magnetic markers (nail and plate types) on the PATH and AHSRA magnetic sensing system, as well as on the noise characteristics observed at different locations on the North Loop. The discussions in this report are based on the preliminary observations from test results during the short proving test period. Those results were not obtained through an optimized process, nor do they present strong statistical significance. Any extension of the summaries should be taken with caution. 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. This system addresses the themes of support for prevention of overshooting on 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. The proving tests at PWRI were performed using one of the Buick LeSabre vehicles that were previously shown at Demo '97, '98 and '99. The only hardware additions to the vehicle are a human machine interface (HMI) display for lane guidance, and AHSRA's lane marker detector for sensing system evaluation. The on-board computer receives lateral measurements from both PATH and AHSRA magnetic sensors. The PATH magnetic sensors were used for most tests performed at PWRI. The AHSRA sensor data were simultaneously recorded for evaluation purpose. The future road geometry is stored in the on-board computer and anticipated by the communication from the AHSRA radio-wave control point markers. The road geometry information is used, in conjunction with the lateral deviation measurements and the vehicle dynamic model, to generate either an automatic steering command to the steering actuator, or a display providing a preview of the future vehicle position (predictor) if the driver does not correct his steering action. The design of this guidance display, which was originally developed for snowplow drivers, was optimized to make it very easy for the driver to steer the vehicle accurately, even in zero-visibility conditions. Furthermore, PATH also demonstrated a smooth switching method that was previously developed, allowing the driver to change between automatic and manual steering control at any location or time that he commands. The lane departure warning system based on the magnetic markers is derived from the "steering guidance" system. A modified predictor computation triggers the departure warning signal. A lane departure warning sounds when the modified predictor estimates that the vehicle will reach the lane boundaries in one second. Lane departure prevention control is a feature that the driver can select. Once activated by the driver, the vehicle automatically switches to "automatic steering control" if the driver continuously ignores the lane departure warning and the vehicle begins to drift into the adjacent lane. By combining the capabilities of automatic steering control, steering guidance display, manual/automatic transition, as well as lane departure warning and prevention control, the PATH lateral system based on the magnetic markers creates a high performance lateral warning/guidance/control system. With such capabilities, the vehicle provides a wide range of possibilities to the driver, from guidance to full automation and from lane departure warning to prevention control, under various curve and visibility conditions. These capabilities also enable PATH to generate substantial test results during the short proving test period.

The report applies these test results to explore the five important issues related to the magnetic sensing and control systems. The main observations from the test results are summarized below:

(1) Automatic steering control consistently maintains small lateral deviation (5 cm maximum on the straight road, and 15 cm maximum on curves regardless of vehicle speeds) as well as small curve transition error. Very small steady state lateral deviation is observed on the curves because of the curvature information.

(2) For the steering guidance case, the driver consistently maintains small lateral deviation (15 cm maximum on the straight road, and 30 cm maximum on curves at various vehicle speeds) despite the fact that the vehicle is manually controlled with simulated zero visibility conditions. The curve transition error is relatively small for all six curve-transitions, and so is the steady state lateral deviation (within 10 cm) on the curves.

(3) For the case when the driver steers based on the lane departure warning alone, the vehicle is consistently maintained close to the lane boundaries even under severe departure conditions. The excursions into the adjacent lane, which usually happened on sharp curves at higher speeds, are generally kept within the width of a tire. The error attributed to the curve transition and the steady state lateral deviation on curves is not significant. No false alarms or missing alarms are observed on the data sets.

A pdf of the complete research report is available at:

http://www.path.berkeley.edu/publications/reports.htm#2001