Gava, I thought you were pretty intelligent, but honestly... People who drive high aren't driving around in cities and shit if they don't have to, they're driving on backroads and highways where people aren't going to see them smoke. Places where you don't need lightning fast reactions. It also impairs you much less than alcohol. Sure, you can drink responsibly and drive, but you can very easily abuse alcohol, without even trying to for that matter, and cause problems with driving. One joint with a friend won't impair your driving that much if you're experienced; same with a bowl or pretty much anything besides a gravity bong.
Your source is incredibly biased. Why would you EVER trust a company created, funded, run by, and monitored by government officials who are trying to justify their anti-marijuana policies over an independent study from an extremely legitimate source such as, oh... Harvard? Clearly if Harvard has any agenda as far as this is concerned, it would be anti-marijuana, but what did they come up with? Oh yeah.
Any more questions?