I noticed the last time we drove through VA on I-81, the digital signs had a message that I really hadn't noticed so much emphasis on before: "Use left lane for passing only."
Driving a while, I saw why. Too many people are in the left lane (81, improbably, is only two lanes on each side). So while you may move, it's a constant go 80, then all the way down to 60, back up to 80 and on and on. Literally, there more cars between Winchester and Roanoke in the left lane than the right the entire time.
So, when a driver who doesn't want to go 70, let alone 80, decides that the one car in front of him is too slow at 65, he'll keep his cruise at 68, which creates a logjam. And then the semi truck can wiggle in because that guy is slowing everyone down, which then slows that left lane down even more when trucks pass each other. Everybody hits their brakes.
Finally, with so much slower traffic on the right, no one ever wants to move back over from the left lane because eventually you'll pass that slower car way up ahead. And because the left lane is always packed, it's hard to get back over from the right.
I also wonder how much the auto cruise factors in and people aren't paying attention that they are piddling along as their car keeps the gap between them.
Overall, we moved fast, pretty much staying in the left lane the whole time. But it was hard, intense driving the whole way. For more than 100 miles in one stretch, I never used the cruise.
The signs identified the problem. But that was all.