Absolutely you are correct that many marijuana users regularly achieve a high under which they ought not drive. One difference between weed and alcohol, is that

Absolutely you are correct that many marijuana users regularly achieve a high under which they ought not drive. One difference between weed and alcohol, is that the marijuana users are more likely to choose not to drive in this state, IE they don't suffer from the same critically impaired judgement that we often associate with drunk driving. IE they are more likely to be respectful of their responsibility as a driver than drivers that have been drinking.