I sort of wonder whether legalizing pot would really result in more stoned drivers than we have now. It is like drunken drivers - it is illegal to drive while under the influence yet it doesn't stop those who do and I wonder if we are not already there with pot.
I believe that police agencies already have the technology to determine if you are driving under the influence of 'clouded' judgement in much the same manner as they can determine that you are under the influence of alcohol.
I just think that legalizing it will knock the bottom out of the criminal enterprise aspect, foster 'locally grown' and 'green' approaches, help divert police costs for drug enforcement into more useful police activities, and reduce the number of people who break the laws to get money to buy pot and other drugs by turning to prostitution, car theft, burglaries and the like. I would hope that once this stuff was legalized we could think about legalizing clinical drug abuse so that those who commit crimes to afford addictive drugs like coke, crack, heroin, etc., could turn to a clinic to meet their needs rather than crime. It was a thought.