Do you think 54% of the general population has alcohol/weed in their system all the time? Because if impairment had no bearing here we would expect the percentage to simply be equal to the rate of drug use in the general population. But if the rate is higher among people involved with accidents then that suggests these drugs likely play a role in accident rates.
And to be frank, I’m skeptical 54% of the population always has either weed or alcohol in their system.
For instance 33% of Americans don’t drink at all and 45% have less than 3 drinks a week. That’s nearly 80% of Americans who will likely not test positive for alcohol the majority of the time. Likewise over 80% of Americans just don’t use weed at all.