While the I-70 is the most mountainous of the three possible interstate routings (crossing the Rockies in the middle of Colorado and some major ranges in Utah), another Northern route, I-80 to Salt Lake City and then I-15 through Las Vegas is actually shorter than most of the other all Interstate routings.....and does not have any major/long mountain stretches. I-80 also has some of the nicest rest areas through Nebraska and Wyoming.