It's 400 miles from Sacramento to LA, so this would add an hour. Both lanes are packed and the speed differential between them is 20mph because the truckers are doing their limit but texting and the cars are going 10 over their 10 higher limit. Relaxing is not possible, it's dangerous no matter what you do and it demands your attention. So might as well be one of the fast ones. There's a sort of recirculation zone that develops behind a truck. They are a rolling roadblock, in a literal sense. Everyone comes rushing up to it and has to go around it, one at a time. There's always about 1 in every 10 who does want to go the limit and he clogs the drain for everyone else. So a line forms on the left - that's where everyone will have to pass. But that lane slows down to the truck speed because the people really jockeying for advantage go in the right lane, right up behind the truck, then pop left to cut the line.

Sometimes of course there's a truck that's 0.5mph faster than another and he decides he's gotta pass. That can back things up for miles.