While drug and alcohol impairment can certainly be a contributing factor in a collision, it is not necessarily always the cause of a given crash. In order to determine if suspected alcohol or drug impairment was a contributing factor in a collision an expert reconstructionist must believe that absent the suspected impairment the collision would not have occurred. 

 

Very rarely will one factor be the sole cause of a collision. Although impairment may have contributed to the collision other factors such as the actions of other drivers, equipment failures, poorly designed roadways and the environment often also play a part in the collision.  Understanding each of these potential factors is critical in determining the actual cause of the collision.