The reason people were doing like 20k's on the highway is this thing called 'Chain Reaction', im sure you learnt about it in year 8 at highschool.
Basically, when erin is up the front doing 90 or so (for a few k's) just so everyone can regroup.. it makes this thing called a chain reaction, causing the cars behind her to break and slow a bit.. and considering we had such a long line, the people at the end of it will have felt the end of the reaction which by the time it hit them, they would have slowed to your apparent 20k's..
ontop of this, we all were traveling in the one left hand lane (which was the right thing to do), and as this lane is used to take exits, people some times had to break to let people in that would like to use the exits.. and i witnessed some of these cars slowing to use the exit, and hesitating which would have sent another 'chain reaction' to the one already sent.
So in theory, the reason why the people at the tail end where doing this 20ks would be causing your dealing wiht at least chain reactions in one.
its simple logic, its commonsense .. wanna go faster, indicate right anf move up the back like me and other members did.
... thats your education for today