"Is there any way to test this accurately? I am concerned about the risk of DUI. Can you please compare to alcohol consumption?"
The police do not stop you because you’ve had alcohol or cannabis they stop you because you’re driving is erratic and then they administer a sobriety test. If you fail the Sobriety test you would be arrested. A breathalyzer test test you for alcohol intoxication but so far we do not have a reliable cannabis breathalyzer test but that does not keep you from being arrested. There was one case, the person admitted to using cannabis before driving but that person was tested and was not impaired at all, yet was still arrested. When the case made it to court the judge threw the case out because the Police had no reason to arrest someone who was not impaired.
You must always know how cannabis affects you before you get in the car and drive because it is illegal to drive under the influence if you are impaired. Know the laws and know your Cannabis and how it affects you before you get in the car to drive and if you plan to be stoned, appoint a designated driver or use Uber or Lift but you never want the mess or the legal problem that come with a DUI.
Alcohol and cannabis cannot be compared because they are completely different drugs and cannot be compared as if they were the same.