Lateral vehicle co-pilot to avoid unintended roadway departure.

Abstract

A detailed investigation of road departure warning systems is presented. A method known as time-to-lane-crossing is compared with rumble strips placed a fixed distance from the road edge, and is found to provide enhanced performance in terms of reduced false warnings and increased warning anticipation. A new approach, called variable rumble strip (VRBS), is proposed as an electronic implementation of rumble strips where the rumble strip threshold is allowed to vary according to the risk of the vehicle departing the road. The rule-based system is realized using a fuzzy logic structure. Performance of the VRBS system is similar to that of the time-to-lane-cross based approach, but requires less sensor information. Performance is measured by comparison with a validation warning set generated by static rumble strip warnings, and subjective assessment of road departure criticality. The algorithms are tested on 12 two-hour driving runs conducted in a full-vehicle driving simulator. One extension of the VRBS system involves an estimate of driver lane-keeping performance used to modify the VRBS threshold adjustment. The estimate, based on the standard deviation of lateral vehicle position, is effective at increasing the anticipatory warning time, and is readily implemented in the fuzzy rule structure. A separate driver modeling effort was undertaken using a system identification approach to develop a driver model, and to update its parameters during driving. Although preliminary driving simulator results indicated that changes in the damping ratio, natural frequency, and DC gain of such a model may be useful indicators of driver fatigue, the identified model parameters were found to not exhibit the expected trends as lane-keeping performance deteriorated on more extensive data sets. Addition of an intervention function is the topic of a second extension, and examines the usefulness of a brake steer system which uses differential brake forces for steering intervention. The steering function achieved can be used to provide limited control authority on vehicle lateral position. Control design models for the vehicle and the brake system are presented. Computer simulation results, using a nonlinear seven degree-of-freedom vehicle model are included, and show the feasibility and limitations of brake steer.