MADD and prosecutors would cite this as there still being a documented increase in collisions.
This study of crash risk found a statistically significant
increase in unadjusted crash risk for drivers who tested
positive for use of illegal drugs (1.21 times), and THC
specifically (1.25 times). However, analyses incorporating
adjustments for age, gender, ethnicity, and alcohol concentration
level did not show a significant increase in levels of
crash risk associated with the presence of drugs. This finding
indicates that these other variables (age, gender ethnicity
and alcohol use) were highly correlated with drug use
and account for much of the increased risk associated with
the use of illegal drugs and with THC.
As someone that would love to represent defendants if this study was admissible, this disclaimer concerns me:
should be viewed in the context of the established
body of scientific evidence on the subject.
This study would not be admissible, and you would not want to rely on it if it was your arse on trial.