Suspected drug driver scenario

I am in my mind palace and trying to figure out this scenario:

I see a man who I suspect is under the influence of cannabis due to a smell coming of the males person, glazed eyes and known for using cannabis regularly.

What powers if any do I have to stop this man getting in a car and driving off?

I know if he is in the car I can go down the route of him being in charge of the vehicle but I’m just thinking are there any preventative powers?