The quickest way to ruin a road trip is to get stuck in traffic. (Photo: Thinkstock) By Brittany Jones-Cooper for Yahoo! Travel You finally did it. You used vacation days, packed up the car, and set off on that cross-country road trip you always dreamed of taking. You’ve programmed your GPS, but what you couldn’t predict was the painful gridlock waiting for you in the next city. Maybe next time you’ll…