Well, but they aren't off the road, are they? They're driving back and forth between NO and Baton Rouge...
So which are there more of? The ones submerged in New Orleans or the ones driving back and forth into the disaster zone. Additionally, upwards of half a million people are no longer commuting because they have no job.

Another question is how we measure the inventory levels. I doubt that gas in one's gas tank is counted, so the sudden dip and rebound could be explained by everybody panicing and topping off the week before Katrina hit and then not buying the following week. This is, admittedly, a short term effect, but it might explain some of this.

FWIW, I am not looking at inventory or production or consumption numbers too closely at the moment because I think that the data is suspect (at best) due to the chaos on the Gulf Coast. I rather expect the numbers will all make a lot more sense around November (barring any further shocks or chaos, of course ... my own personal force majeure clause).