Absolutely, put one of the older boys behind the wheel. When you're on a long trip, give another one responsibility for navigation - turn off the GPS and get out the map!
In the meantime, is there any pattern or common problem in the battles? Friends of mine used even and odd dates to determine who sat in which seat position (only two kids in that family so you'd need to adjust for your purposes) - if there's a common theme, is there some way you can devise a plan for defusing it before it starts?
It's hard to believe when the battle is raging, I know, but you are fortunate to still have children that old at home and willing to get in the car with you!