I'll second the "short trip" posts, because I have the opposite -- my commute is 47 miles each way, most of it highway. Even going through the foothills and over the Blue Ridge Mountains, my long trip and highway commute net me 38 MPG without thinking about it, and my best tank (of only four thus far) was 39.5 MPG.

So, it seems like the best idea would be to move far, far away from your job, like me! (I'm kidding! I'm kidding!)