So we are up something like a buck thirty per gallon from this time last year. The commute to my new job has knocked a few MPG off what I used to get. In the Vibe I used to do 33-34 most of the time, but I have been getting more like 30. This is the worst I have consistently gotten. With gas prices crazy high I have been doing some mild hypermiling and cutting my expressway speed down to 60 or 65. At my fill up this morning I calculated 33.6mpg for the tank. Not too bad.
Say you drive 10 miles on the highway. Going at 70mph it would take you about 8.5 minutes, but 60 would take an extra 1.5 minutes. Since your MPG decreaces dramatically above 55mph. I only have about 5 miles on the expressway, so according to this site I can save about $60 a year by doing 60 instead of 75 and it will only take 1 minute more each day.
All time worst was 24mpg pulling a canoe trailer to Grand Rapids and back. All time best was 37 on an all highway cruise down from the UP at 70-ish .
I also need to get better about taking the roof rack off. During the summer we carry canoes a couple times a week, so it usually gets left on. It only takes a couple minutes to put it on or take it off. A roof rack can drop MPG by about 10%.