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An important new technique in safety engineering for complex systems is the fault tree analysis method. The results of a motor vehicle brake system safety analysis using the fault tree technique are described. The work is directed toward the identification and ranking of brake system failure modes which may be critical as accident causation factors. Safety criticality for each failure mode is defined as the product of probability of occurrence and severity of effect on vehicle control. Failure data for the brake system components are obtained from maintenance and repair records of a large automobile leasing fleet. An effect scale is developed using a method for pooling expert judgements to obtain the relative ranking of various brake faults as to accident causation potential. The fault tree structure is employed to combine probability and effect to obtain the safety criticality value of each fault.

An evaluation of the applicability of braking control systems for highway vehicles was carried out. Elements of the study included development of a theory of vehicle response in braking maneuvers, design of logic for a braking control system, incorporation of the control in a hybrid computer simulation of a motor vehicle, and evaluation of control system performance. Benefits of braking control systems are illustrated in terms of improvement in stability characteristics (rear-wheel control) and in directional control (four-wheel system).