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|Head-On Traffic Accident
A head on traffic accident occurs when the front of one vehicle collides with the front of another. These types of
accidents are extremely dangerous because of the cumulative speed affect of vehicles colliding in opposite
directions. Accident reconstruction experts often refer to the combined difference in speed as closing speed or
For example, if two vehicles collide head on with each traveling at 30 MPH, then the closing speed between the two
vehicles would be equal to 60 MPH. If the same two cars were to collide, with one of the one of the vehicles stopped,
then the striking vehicle would need to be traveling 60 MPH to equal the same closing speed.
Another reason why head on accidents are so dangerous is because they often involve large and abrupt changes in
velocity. Expert accident reconstructionists refer to a vehicle's change in velocity as Delta-V. Sudden and
considerable changes in velocity have been directly linked to injury causation.
The number one reason for a head-on collision is improper lane use by one of the drivers. In other words, one driver
generally crosses left of the lane divide into oncoming traffic prior to the crash. Improper lane use is often the product
of inattentive or distracted driving.
Our accident reconstruction experts can often solve for the impact speeds of vehicles involved in a head on crash
through various equations based on the conservation of momentum and dissipation of energy.
In addition, by quantifying the Delta-V of one vehicle, our experts can solve for the Delta-V of the second vehicle
involved in the accident.
A vehicle's total Delta-V, or change in velocity due to a collision, is an indispensable resource for expert accident
reconstructionists. Many vehicles have the ability to record longitudinal Delta-V if the vehicle is involved in a serious
crash. The recording is usually stored in a component of the vehicle's airbag control module called an event data
recorder or EDR.
If the Principal Direction of Force, or PDOF exerted on a vehicle is known, and the longitudinal Delta-V is recorded
during a crash, then the total Delta-V experienced by a vehicle during a collision can be derived.
When vehicles collide head on, the post impact
motions of the vehicles are dictated by
momentum. Momentum is a vector quantity, in
that it has both a size and direction.
An accident reconstruction expert can quantify
momentum by multiplying a vehicle's weight by its
speed. In the above illustration, if we assume
that both vehicles weighed about the same, then
we know that the blue car was traveling much
faster at impact due to the post-impact
trajectories of the vehicles.
|Head-on collisions make up only 2% of US
crashes, but account for over 10% of
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