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The use of force against a driver or occupant of a moving vehicle by a law enforcement officer has been a source of public criticism and, in some cases, results in the criminal prosecution of the officer. Some law enforcement executives responded by implementing policy against this specific use of force. The Police Executive Research Forum (PERF) suggested law enforcement agencies adopt a policy that maintains a “strict[ly] prohibition” against shooting at someone in a vehicle unless the person in the vehicle is using or threatening deadly force with something other than the vehicle itself (#8). The policy suggestion did not discuss the potential lethality, or lack of, associated with a moving vehicle.

In the period following the policy suggestions and adoption, terrorists and other active killers began to increase the use of motor vehicles in their attacks. It is unknown if the adopted or suggested PERF policies considered such vehicle criminal/terrorist applications in their suggestions, and/or if a revision is planned by PERF or any agencies adopting a similar policy. It is also unknown if any of the law enforcement executives and/or PERF regarded any human performance conditions in their proposals or have incorporated the necessary training to address a moving vehicle threat in support of their policy.

“. . . people will act to save themselves regardless of imposed policies, so any rule that attempts to transcend a person’s legitimate right to protect their own life will be immediately disregarded and is doomed from the onset.” –Sid Heal

In addition to the expected human performance conditions (startle reactions, stress responses, orienting/decision-making, etc.), a law enforcement officer may also experience perceptual conditions referred to as “looming” and/or “lateral compression”.


As an object (vehicle) approaches a human subject (observer) directly, that object begins to fill the observer’s visual field symmetrically and exponentially as the object closes the distance between itself and the observer. At short distances, the vehicle image growth expansion rate perceptually explodes. As the object-observer distance closes by one half, the object image size doubles. When that distance is reduced in half again, the image size doubles in half the time. Though the looming principle is associated with moving objects in general, a robust finding relating to motor vehicles is understood. One researcher summarized “looming” as, “In simple terms, the image of the object grows on the viewer's retina (Lawrence, C., 2014).”

As a moving vehicle travels directly towards an observer, perhaps a law enforcement officer, the observer begins to not only perceive the vehicle as a potential lethal threat, but also moving more quickly towards them than it may be in reality (Vagnoni, Lourenco, & Longo, 2012). This perception may then influence decision-making (the lethality potential and the timing required to take action and respond). Perception may also vary between individuals, including witnesses and other law enforcement officers, who may also be present in the general area but not on the observing law enforcement officer’s identical plane of view. As a result of the varied perception, they may not make the same decisions, use the same force, or view the potential threat similarly.


Should the scientific method be employed when objectively analyzing a law enforcement use of force? Why, or why not?

Can a written policy override a sympathetic nervous system response? Why, or why not?

Are trained law enforcement officers subject to the same human performance conditions as an untrained person?

Should physiological functions be regarded when objectively analyzing a use of force for reasonableness? Why, or why not?

How should an investigator view varied witness accounts when analyzing a law enforcement use of force for reasonableness?


Lawrence, C. (2014). Force Science Institute.

Vagnoni, Lourenco, & Longo (2012). Threat modulates perception of looming visual stimuli. Current Biology, Vol. 22, No. 19, R826.

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