Yeah, we have the 'fuel here' problem too. Still, as you said, adjustments can be made. Some minor, some not so. Last night, for instance, instead of driving I-80 from Laramie to Cheyenn, THEN south to Denver, we took 287 from Laramie to Ft Collins. Saved 26 miles. Route is mostly down hill, so saved fuel. Speed limit is 65 all the way into Ft Collins (then 35, and about 15 stop lights if you hit them all bad) before you are on I-25. Saved about 35 minutes, since we didn't have to climb that hill between Laramie and Cheyenne.
On the other hand, if we'd taken the interstate around the Ozarks instead of the highway through, we'd have heard about it.