[ There have been many changes to this law, most recently in 2018, see history, below]
Prosecutors routinely decline to prosecute negligent drivers who kill/injure. Nearly without exception, they will only seek homicide (i.e. negligent homicide, or manslaughter) / aggravated assault charges if the driver is impaired. Short of that, the hurdle, in the minds of prosecutors, is very very high.
Arizona has no vehicular homicide law, it does however since 1998 have a law, §28-672, ” Causing serious physical injury or death by a moving violation” (and some companion laws 28-675 and 6 which work in an analogous fashion). The catch is that in order to be charged with 28-672, the driver must have been engaging in one or more of a specific list of infractions. For example, running a red light. Continue reading 28-672 in the news