I don't see anybody mentioning this, but I drove the length of SD the Memorial Day week. Traffic was light, but we ran into a ton of construction zones throughout the week.. None of it was marked by the local (at home) AAA office on the road maps they gave us.
Mostly, we saw orange cones and few, in any, workers. Some of these days were weekends. But there were construction zone speed limits - enforced? I don't know what it will be like as the summer continues.
There were MILES when the number of lanes was reduced.
You might want to keep this in mind if you are planning tight driving schedules. Maybe those who live in SD can shed more light on this.