Vehicle Risk Assessment & Physics 101

10/25/2011 | By David David Dickinson, Delta Scientific


When evaluating the security risk for a car bomber or crasher for a given facility, focus on the weights and velocities of vehicles that could be used to attempt penetration into sensitive areas. 

A vehicle moving towards a barricade has a certain kinetic energy, the major measure of how much "hitting power" it possesses.  Mathematically, kinetic energy is derived from the vehicle velocity and its weight (mass).  On impact, some energy is converted to heat, sound and permanent deformation of the vehicle.  To stop the vehicle, the barricade must absorb the remainder. 

The remaining energy varies depends primarily on the velocity of the vehicle at the moment of impact.  The amount of kinetic energy possessed by a vehicle changes by the square of its velocity.  A vehicle moving at 50 mph has 25 times as much kinetic energy as at 10 mph.  An armored car weighing 30 times as much as a Toyota moving at 10 mph has less hitting power than the Toyota moving at 60 mph!

Because of the relationship of velocity to the total kinetic energy, every effort must be made by the security engineer to force a vehicle to slow down before it reaches the barricade.  The most frequently used technique is to require a sharp turn immediately in front of the barrier.  When vehicle speed is reduced by 50 percent, "hitting power" is reduced four times.  If the speed is reduced 2/3rds, the force of impact is reduced nine times.

 Upon designing a way to slow down vehicle approach, precautions should also be taken that the attacking car cannot make a "corner cutting shot" at a barricade.  Often, only a light post defines a turning point and a speeding car can take it out and not even hesitate.  Knolls and other impediments should be considered. Failing to understand this and not using the proper equipment to counter threats leads to a false sense of security.

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