ANOVA – Analysis of variance.

Additional driver – Family or friends of the primary driver who drove the subject's vehicle and were not involved with the in-processing.

Associative Factors – Any environmental or vehicular factor where direct causation to crashes, near-crashes, or incidents is not possible to attain but correlation may be determined.

Backing crash – A crash that occurs while the driver's vehicle is in reverse gear.

Chase vehicle – Vehicle designated for locating (through GPS or other means) and downloading data from subject vehicles.

Contributing factors – Any circumstance that leads up to or has an impact on the outcome of the event. This term encompasses driver proficiency, willful behavior, roadway infrastructure, distraction, vehicle contributing factors and visual obstructions.

Crash – Any contact with an object, either moving or fixed, at any speed in which kinetic energy is measurably transferred or dissipated. Includes other vehicles, roadside barriers, objects on or off the roadway, pedestrians, cyclists, or animals.

Crash-Relevant Event – A subjective judgment of any circumstance that requires, but is not limited to, a crash avoidance response on the part of the subject-vehicle driver, any other vehicle, pedestrian, cyclist, or animal that is less severe than a rapid evasive maneuver (as defined in near-crash event), but greater in severity than a “normal maneuver” to avoid a crash. A crash avoidance response can include braking, steering, accelerating, or any combination of control inputs. A “normal maneuver” for the subject vehicle is defined as a control input that falls outside of the 95 percent confidence limit for control input as measured for the same subject.

Conflict Type – All crashes, near-crashes, crash-relevant conflicts and proximity conflicts were categorized based on the initial conflict that lead to the crash that occurred or would have occurred in the case of near-crashes and incidents. There were 20 types of conflicts used which are as follows: conflict with lead vehicle, following vehicle, oncoming traffic, vehicle in adjacent lane, merging vehicle, vehicle turning across subject-vehicle path (same direction), vehicle turning across subject-vehicle path (opposite direction), vehicle turning into subject vehicle path (same direction), vehicle turning into subject-vehicle path (opposite direction), vehicle moving across subject-vehicle path (through intersection), parked vehicle, pedestrian, cyclist, animal, obstacle/object in roadway, single-vehicle conflict, other, no known conflict, unknown conflict. This list was primarily from National Automotive Sampling System (NASS) General Estimates System (GES) Accident Types.

DAS – Data Acquisition System.

Data Reduction – Process by which trained Virginia Tech Transportation Institute (VTTI) employees reviewed segments of driving video and recorded a taxonomy of variables that provide information regarding the sequence of events leading up to the crash, near-crash, incident, as well as environmental variables, roadway variables, and driver-behavior variables.

Driver distraction - When a driver has chosen to engage in a secondary task that is not necessary to perform the primary driving task.

Driver Impairment – The driver's behavior, judgment, or driving ability is altered or hindered. This includes drowsiness, use of drugs or alcohol, illness, lack of or incorrect use of medication, or disability.

Driver Proficiency – Whether the individual's driving skills, abilities, or knowledge are inadequate. This specifically refers to whether the driver appeared to be aware of specific traffic laws (i.e., no U-turn), whether the driver was incompetent to safely perform a driving maneuver (i.e., check for traffic before pulling out on a roadway), unaware of the vehicle's turning radius, or performs driving maneuvers under the incorrect assumption that it is safe, (i.e., drives over a concrete median).

Driver-Related Inattention to the Forward Roadway – Inattention due to a necessary and acceptable driving task where the subject is required to shift attention away from the forward roadway. (e.g., checking blind spots, center mirror, instrument panel).

Driver Reaction – The evasive maneuver performed in response to the precipitating event.

Driver Seat Belt Use – Variable indicating if the subject is wearing a seat belt during an event.

Drowsiness – Refers to a driver who is either moderately to severely drowsy, as defined by Wierwille and Ellsworth (1994). A driver who is moderately drowsy will exhibit slack musculature in the facial muscles and limited overall body movement as well as a noticeable reduction in eye scanning behaviors. A severely drowsy driver will exhibit all the above behaviors as well as extended eye lid closures and will have difficulties keeping his/her head in a lifted position.

EDR – Electronic data recorder.

Epoch – Typically, a 6-second period of time that was selected randomly to allow for the observation of normal, baseline driving.

Event – A term referring to all crashes, near-crashes, and incidents. The “event” begins at the onset of the precipitating factor and ends after the evasive maneuver.

Event Nature – Classification of the type of conflict occurring in the event (e.g., conflict with lead vehicle, conflict with vehicle in adjacent lane).

Event Severity – Classification of the level of harm or damage resulting from an event. The five levels were crash, near-crash, crash-relevant, proximity, and non-conflict.

FARS – Fatality Analysis Reporting System.

FOV – Field of view.

FV – Following vehicle .

GPS – Global Positioning System – used by data reductionists to locate participant vehicle for information on an event.

Inattention – Any event or epoch where drowsiness, driver-related inattention to the forward roadway, driver secondary tasks, or non-specific eyeglance away from the forward roadway were identified as a contributing factors to the event.

Incident – Encompasses the event severities of crash-relevant conflicts and proximity conflicts.

IVI – Intelligent Vehicle Initiative .

IR LEDs – Infrared light-emitting diode.

Invalid Trigger – Any instance where a prespecified signature in the driving performance data stream is observed but no safety-relevant event is present. See Appendix C for a more complete definition of triggers.

LV – Lead vehicle.

MVMT – Million vehicle miles traveled.

NHTSA – National Highway Traffic Safety Administration.

Naturalistic – Unobtrusive observation. Observation of behavior taking place in its natural setting.

Near-crash – A subjective judgment of any circumstance that requires, but is not limited to, a rapid, evasive maneuver by the subject vehicle, or any other vehicle, pedestrian, cyclist, or animal to avoid a crash. A rapid, evasive maneuver is defined as a steering, braking, accelerating, or any combination of control inputs that approaches the limits of the vehicle capabilities.

Non-Conflict – Any incident that increases the level of risk associated with driving, but does not result in a crash, near-crash, or incident as defined. Examples include driver-control error without proximal hazards being present, driver-judgment error such as unsafe tailgating or excessive speed, or cases in which drivers are visually distracted to an unsafe level.

Non-Subject Conflict – Any incident, crash-relevant conflict, near-crash, or crash that is captured on video but does not involve the subject driver. Labeled as a non-subject conflict but data reduction was not completed.

Onset of Conflict - Sync number designated to identify the beginning of a conflict; also known as the beginning of the precipitating factor.

ORD – Observer Rating of Drowsiness; measured on a scale from 0 to 100 in increasing severity of drowsiness. Based on Wierwille and Ellsworth (1994), who developed this procedure where observable behaviors were identified to allow data reductionists to reliably and consistently rate the drowsiness of drivers using post-hoc video data reduction.

Precipitating factor – The driver behavior or state of the environment that initiates the crash, near-crash, or incident, and the subsequent sequence of actions that result in an incident, near-crash, or crash.

Primary Driver – The recruited participant designated as the main driver of his or her own vehicle or a leased vehicle

Proximity Event – Any circumstance resulting in extraordinarily close proximity of the subject vehicle to any other vehicle, pedestrian, cyclist, animal, or fixed object where, due to apparent unawareness on the part of the driver(s), pedestrians, cyclists, or animals, there is no avoidance maneuver or response attempted. Extraordinarily close proximity is defined as a clear case where the absence of an avoidance maneuver or response is inappropriate for the driving circumstances (including speed, sight distance, etc.).

Pre-Incident Maneuver – The maneuver that the driver was performing immediately prior to the event. The importance of this is to record what the driver was doing before the precipitating event occurred.

Precipitating Factor – The action of a driver that begins the chain of events leading up to the crash, near-crash, or incident. For example, for a rear-end striking collision, the precipitating factor most likely would be lead vehicle begins braking (or lead vehicle brake lights illuminate).

Secondary Task – Task, unrelated to driving, which requires subjects to divert attention resources from the driving task, e.g., talking on the hand-held device, talking to passenger, eating, etc.

Rear-end striking – Refers to the subject vehicle striking a lead vehicle.

Rear-end struck - Refers to the subject vehicle being struck by a following vehicle.

Sideswipe – Refers to either a vehicle in the adjacent lane changing lanes into the subject vehicle lane or the subject vehicle changing lanes into an already occupied adjacent lane.

SV – Subject vehicle.

Time-to-Collision (TTC) – A calculation that estimates the moment of impact. This calculation uses radar data (either forward or rear) to obtain measures of range and range-rate.

Trigger/Trigger Criteria – A signature in the data stream that, when exceeded, 90 seconds of video data (60 seconds prior and 30 seconds after the data excedence) and the corresponding driving performance data are copied and saved to a database.  Trained data reductionists assessed these segments of video and driving performance data to determine whether this segment of data contained a safety-relevant conflict (i.e., crash, near-crash, or incident) or not.  Examples of triggers include a driver braking at 0.76 g longitudinal deceleration or swerving around an obstacle, obtaining a 0.8  g lateral acceleration. For a more complete description of triggers, see Appendix C.

US DOT – United States Department of Transportation.

Valid Event or Valid Trigger – Those events where a specific signature in the data stream was identified and viewed by a data reductionist and deemed to contain a safety-relevant scenario. Data reductionists recorded all relevant variables and stored this data in the 100-Car Study database.

Vehicle Run-Off-Road – Describes a situation when the subject vehicle departed the roadway.

VDOT – Virginia Department of Transportation.

Virginia Tech Motor Pool – An extension of the Virginia Tech Office of Transportation.

VTTI – Virginia Tech Transportation Institute.

Visual Obstruction – This variable refers to glare, weather, or an object obstructing the view of the driver that impacts the event in any way.

Willful Behavior – The driver knowingly and purposefully drives in an unsafe or inappropriate manner. Includes aggressive driving, purposeful violation of traffic laws, use of vehicle for improper purposes (i.e., intimidation).