Came across this today... http://online.wsj.com/article/SB10001424052748704688604575125510326010610.html
A few things may be a bit off in it, but I like how someone with influence is finally agreeing that people drive a specific speed despite what is posted, not a specific amount above the limit.
So they've discovered the 85th percentile rule!
I'd be interested to read the full report. Particularly, a breakdown of what certain speed limits are and an what the measured speeds were.
I noted that they used "average" speed to describe their speed survey findings. This means that the 85th percentile speed, which is supposed to be used for setting speed limits according to various engineering handbooks and guidelines, would likely be higher than those indicated in the article.