Although I hear a lot of media hand-wringing about fuel prices, the interstate speeds in my area (Central Indiana) continue to average 10-15 mph above the posted limits.
Apparently the value of time still exceeds the potential fuel savings.
Same thing here in Austin TX. Not just that, but one person per vehicle is the norm. There are some people driving gas hogs that exceed the speed limit by 10+ MPH every day. We see some of the same vehicles every day, and the same ones are speeding.
I drive a van pool. There are six current members, and will pick up a new rider next month. $25.00 per month for members, and I don't pay a cent. Primary drivers have to clean and make sure the van is maintained, records are properly posted, so we have a "free" ride.