The independent evaluation of a roadway departure crash warning system will include assessing the safety benefits and driver acceptance of the system, each of which is influenced by the timing of the warning algorithm. As such, a means to assess this timing is necessary. The crash prevention boundary (CPB) facilitates this. This paper develops analytic CPB relations for two common roadway departure scenarios: lane drift on a straight road and failure to negotiate a curve. The relations are expressed as the required lateral acceleration versus "steering time" and "time to road departure," and include only the essential kinematic variables. The simplicity of the expressions allows an analyst to gain insight into the interaction of the various kinematic variables and to readily apply the expressions to assess both the timing of the warning algorithms and driver responses to the alerts.
Abstract