Driving high and driving drunk are not even in the same ball park.
Driving Drunk = swerving, speeding, blackouts, wrecks, DUIs
Driving Stoned = driving too slow, missing exits, stopping too often for munchies, avoiding cops like the black plague.
I love puffing when I have to drive a long distance on the highway. I used to drive to Denver every couple of months (about 900 miles away). I could puff the entire way and only ever stop for gas and the bathroom. About 13 hours strait driving. Weed made the drive interesting and it would fly by. Weird thing about weed, even though it usually makes you sleepy, for some reason when driving stoned I tend to stay more alert and never get the urge to doze off while driving like I do sometimes when I'm straight. Just like gyphon said.
Also, if you ever do start to feel drowsy on a long drive, take a few tokes on the old pipe and bam, you aint drowsy no more. Just nicely toasted and ready for a few more hours of pure zoning out and driving.