A/C vs. Rolling Down Your Windows

I guess, according to Slate, this is the rule of thumb when trying to determine which uses less gas--air conditioning or rolling down your windows:

1. In the city, roll down your windows.
2. On the freeway, use the a/c.

The deal is that on the freeway, rolling down your windows creates so much drag that you use more gas than you would if you just had the a/c on and the windows up.

And don't tell me this blog isn't here to help you.