It's an Ozone Action Day in Austin. It's one of those "hot, sunny, still days when conditions are most favorable for the accumulation of unhealthy levels of ground-level ozone."
People are supposed not use exhaust-producing tools (lawnmowers, etc.), drive only when necessary, and carpool.
This weekend is also the 2006 Republic of Texas Biker Rally, where thousands of non-carpooling vehicles will descend on the capital of Texas.
I find this funny.