In my daily communte, I go over a signficant hill very close to where I get on the freeway each morning. I would estimate it’s about 2 miles up to the summit and 2 miles back down. This section of the freeway is 3 lanes (the entirety of this freeway changes between 2 to 3 to 2 to 4 to 3 to 2 lanes in its 20-some mile run). It is also frequented by large trucks who frequently can go no faster than 30 mph. It’s a steep hill, but I can do 65 going up it. I have observed thusly:
The Rock: When large truck is in the righthand lane (“slow” lane), the traffic flows like a river around it. The water gets stuck behind the rock and then has to move sideways to avoid it, which slows the water immediately adjacent. This seems to slow the whole freeway down next to the truck and then everyone speeds up as soon as you pass it.
The Iceberg: Sometimes, there is too much traffic in the right lane for the trucks to get over into it and they get stuck in the middle lane. Curiously, this seems to actually cause less backup, because people use the left/fast and right/slow lanes to go around the truck, essentially creating two escape routes.
It makes me wonder about the fluidity of traffic and the group mind as people try to avoid the trucks.