As an afterthought, if you really, really, really wanted to keep your sheet in the format it's in now then what you could do is split the formula up.

For example, you could have some hidden rows off the bottom of each week sheet which total up the fuel for each state across the 4 trips, then the summary sheet would just have to total up the states for each week.

If you want I can post back a modified version of your example, showing how this would work, but you'd have to wait until tomorrow ... it's midnight here in the UK and I'm off to bed.