The motive force was beneath the impact: Evidence need to demonstrate the driver was impaired, commonly by way of a blood alcohol focus (BAC) of 0.08% or better or proof of drug impairment. Legal regulations vary from condition to state, as do legal punishments, but felonies carry a heavy penalty: https://dui-lawyers.usattorneys.com/what-are-common-ways-that-police-officers-make-mistakes-during-dui-investigations-in-florida/