If you're crazy, as many of you remember me to be, I submit "The Concrete Canyon":
http://img142.imageshack.us/img142/6105/loop1ez1.png
Just under 7 miles, I beleive my record is around 6 minutes. It's been a long time. DO IT COUNTER CLOCKWISE, the expansion joints are murder in the other direction.
Do it at 2am and tell your family that you love them before you go.
If you do it a reasonable speed, it's a good way to see the town.
The greatest rush in columbus driving; flat out under high street. I've only mustered a hair over 140 through here. Again, don't do this, it's a real bad idea, I'll never do it again. Traffic joins the highway here.
http://img124.imageshack.us/img124/5882/loop1gt8.png