Road Accident Dynamics: Phases and Impact Classification

Accident Phases

An accident is an event that unfolds in time and space, typically divided into three distinct phases:

Perception Phase

This is where the driver or pedestrian perceives danger. It includes:

• Possible Perception Point: The time and place where an abnormal situation could be perceived by an ordinary person.
• Real Perception Point: The time and place where the driver or pedestrian actually perceives the abnormal situation for the first time.

Decision Phase

This phase begins after perception, when the driver decides on a course of action to mitigate the perceived dangers. It involves information processing, rationalization, and decision-making.

Evasive actions can be categorized as:

• Simple Passive Evasion: Actions like honking the horn or flashing lights.
• Simple Active Evasion: Actions such as decreasing speed, stopping, or increasing speed.
• Complex Evasion: A combination of actions, e.g., slowing down, turning, and honking the horn simultaneously.

Conflict Phase

This is the period during which the accident physically occurs or is caused. Key elements include:

• Area of Conflict: The zone where the possibility of an accident develops.
• Point of Conflict: The exact location where physical contact occurs between vehicles or objects, resulting in the maximum impact.
• Final Position: The resting position of the vehicle(s) or objects involved after the accident.

Accident Modes of Production

Accidents can manifest in various ways, categorized by their mode of production:

Shock

Contact between a vehicle and a fixed road component.

Overturning

An accident involving a single traffic unit where the vehicle rolls.

• Roll-over (Bell): The vehicle spins on its transverse axis.
• Roll-over (Barrel): The vehicle spins on its longitudinal axis.

Run-off-road

The vehicle leaves the roadway while circulating. This can be a simple event or a complex result of a preceding accident.

Collision Types

Collisions are complex accidents involving contact between moving units, or between a vehicle and a pedestrian. They are further classified by the point and angle of impact:

Frontal Collisions

• Central: Approximate alignment of the vehicles' longitudinal axes.
• Eccentric: Axes are parallel but do not align.
• Angular: Longitudinal axes form an angle less than 90 degrees.

Side Impact

At least part of one vehicle's side is impacted.

• Perpendicular: Vehicle axes are at 90 degrees, subdivided into anterior, central, or posterior impact points.
• Oblique: Angle is greater than 90 degrees, divided into front, middle, or posterior impact points.

Reflected Collision

Multiple contacts between the same traffic units.

Rear-End Collision

Two vehicles, where the front of one collides with the back of another.

Sideswipe

Lateral contact between two traffic units.

• Positive: Vehicles moving in opposite directions.
• Negative: Vehicles moving in the same direction.