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111 actual severity. The actual outcome severity which is the result of the actual event (e.g., DeltaV and minimum time to collision). crash. Any contact that the subject vehicle has with an object, either moving or fixed, at any speed in which kinetic energy is measurably transferred or dissipated. Examples and hints: Includes other vehicles, roadside barriers, objects on or off of the roadway, pedestrians, cyclists, or animals. In the rear-end collisions in the present data set, only vehicle-to- vehicle contacts are classified as a crash. driver distraction. Diversion of attention away from activities critical for safe driving to one or more activities that are not critical for safe driving. A type of driver inattention. driver inattention. A mismatch between the current attention allocation (distribution) and that demanded by activities critical for safe driving. Includes driver distraction. eyes off path. Glances away from the vehicleâs path, the direc- tion of the vehicleâs travel. Includes transitions toward an off-path location and eye closures greater than 1â3 second. FCW. Forward collision warning system. glance. Time from the moment at which the direction of gaze moves toward an area of interest to the moment it moves away from it. A glance consists of transition time toward a target plus the subsequent dwell time on that target (ISO 15007). inopportune glance. A glance away from the forward path at an inappropriate time. lead vehicle (LV). The vehicle preceding the subject (partici- pant) vehicle in the same lane. Lead-Vehicle Precrash Scenarios. A classification of the crash according to precrash Scenarios 22â26 from Najm and Smith (2007) corresponding to rear-end crashes in National Automotive Sampling System (NASS) crash databases. near crash. Any circumstance that requires a rapid, evasive maneuver by the subject vehicle or any other vehicle, pedes- trian, cyclist, or animal to avoid a crash. A rapid, evasive maneuver is defined as steering, braking, accelerating, or any combination of control inputs that approaches the limits of the vehicle capabilities. Examples and hints: As a general guideline, subject-vehicle braking greater than 0.5 g or steering input that results in a lateral acceleration greater than 0.4 g to avoid a crash constitutes a rapid maneuver. odds ratio (OR). A measure of association between an expo- sure and an outcome. The OR represents the odds that an outcome will occur given a particular exposure compared with the odds of the outcome occurring in the absence of that exposure. For example, the odds ratio of having a critical event (crash, near crash, or both, depending on the analysis) is calculated as a function of various predictors, such as glance characteristics or distraction types. potential severity. The severity which can potentially result from a scenario, based on mathematical simulations. precipitating event. The state of environment or action that began the sequence under analysisâthat is, what state or action by this vehicle, another vehicle, person, animal or non- fixed object was critical to this vehicle becoming involved in the crash or near crash? This is a vehicle kinematic measure (based on what the vehicle does; an action, not a driver behavior). It occurs outside the vehicle and does not include factors such as driver distraction, fatigue, or disciplining a child. secondary task. A task, unrelated to driving, that requires drivers to divert attention from the driving task (e.g., talking on a cell phone, talking to passenger[s], eating). subject vehicle (SV). The participantâs instrumented vehicle. That is, the following vehicle in the Lead-Vehicle Precrash Scenarios. time headway (THW). Elapsed time between when the front of the lead vehicle passes a point on the roadway and when the front of the following vehicle passes the same point. time to collision (TTC). The time left to crash before two vehi- cles collide (rear-end collision) if no evasive action is taken. Glossary
112 vehicle kinematics. The description of the motion of vehi- cles. For example, the description of the trajectories of the subject (driverâs) vehicle and the lead vehicle and their dif- ferential properties, such as velocity, acceleration, and time to collision. VTTI. Virginia Tech Transportation Institute. what-if simulations. A process of changing parameters (e.g., removing evasive maneuvers), applying alterna- tive driver behaviors, and analyzing outcomes of such simulations.
