I've studied neurology basics, and it is difficult for me to decide which one, perhaps it is micture of both, un and sub consciousness.
Let me point to the typical as I think mode of tailgaters (I only guess because I am not one) so called "autopilot" when one switch off and focus only on the stop light of the car in front. This can be observed in cases when locked on to the tailgating mode, all other lanes are free to move and drive faster even within limit and surely free of obstacle of slower cars in front, but those drivers on autopilot persist and do not notice of the opportunity to change lane. Often they do tailgate for a long distance without changing lane which is free for some time and only when you decide to do so or come from behind, they come suddenly in front of you. This is partially subconscious. Our peripheral vision is sensitive to movement, their brain register this, they immediately notice that the object they notices (you) moves on or into free lane, they make immediately reactive rather than fully conscious and rational decision and they move dangerously in front of you. I believe that if they drove not on autopilot, they would long before you decided and changed lane.
I believe that such sub/un counscious behavior is a result of poor driver training. Proper training enable much better and counsious decisions and faster.