Traveling at 70 miles per hour, without stopping, it takes almost a full business day ... 7.3 hours ... to drive the longest highway in Arizona from end to end. US 191 in Arizona pretty much runs border to border, starting at the international, Mexican border and ending in Utah, near the state line. Gas up, grab some snacks and use the restroom before you leave. Make sure you have a camera and maybe a jacket too as you're going to travel from one extreme to another in terms of scenery and climate.