An understated point.

On freeways, each lane tends to develop its own speed, and at 4+ lanes the cognitive load starts to overwhelm me, especially when the relative speed difference between neighboring lanes is very high. At this point anyone in a slow lane may decide to try to pull out into the fast lane, or someone from the faster lanes might try to squeeze in to the queue of waiting cars; meanwhile if you try to unilaterally lessen the speed difference, the people behind and around you will get antsy and aggressive, often defeating the point.

These situations are some of the most dangerous that most driver experience: high speeds, large discrepancy between speeds, and limited escape paths.