If your wife doesn't suspect your anal retentiveness in maximizing mpg, you could say,
"You know honey, life moves by so fast, whatd'ya say we take the scenic route? And because I love you and the kids, I'm going to drive very responsibly to maxamize our safety."
If she says,
"Oh darling, I married the best man in the world" Well, you're in buddy.
If she says,
"That's #@$% and you know it. You don't care about us, you just want to get the most %$#@ mileage you can out of that POS Honda." In that case the jigs up and you have to take the mileage hit.
