The perception by Law Enforcement Officers that someone may be operating a motor vehicle under the influence of Cannabis with an active THC blood concentration of 5ng/ml or more can result in their transport to a testing facility where blood will be drawn whether they agree to submit to the blood draw or not. At the time of transport their vehicle may be impounded. If the blood test results are to that standard or higher, it is 'per se' proof of impairment that will result in conviction for DUI, fines, drug treatment or more in addition to any attorney fees.
No one wants to be on the road with anyone who is impaired by whatever reason. Conversely, no one wants anyone who is not actually impaired to be deprived of their Freedom or property. The 5ng/ml of blood limit is not a clear and consistent indicator of impairment based on current science, but will result in conviction.