My Father 90 plus percent of the time ,took us on a family vaction over the 4th of July time span.
Now that was 45 to 55 years ago and there were fewer people and cars, but the freeway was mostly not complete.
I remember well, the train of cars going up the Rockies at 40mph and 65 going down, curves and all.
My last camping trip with him was '95 going to Sturgis, SD the week before the Sturgis Ralleye
A lot of traffic and most interesting.