So what if she waits some extra time when you are driving 70mph? You are only traveling at 14.6ft/s less doing 70 than 80. Your "scenario" is flawed if you only account for speed. Where are the fact that you have brakes and that you as the driver doing 80mph ARE paying attention to the road? You will have a better reaction time and can slow down to avoid the situation because you are NOT being distracted.
They have proven people's reaction times in cars when they are doing various events while driving.
http://www.visualexpert.com/Resources/reactiontime.html
I think they should up the speed some because 85 is a bit low considering most of the time I have ever driven either down 75 to FL or up 85 to Greenville, my average cruising speed is 85-90 with other cars in front and behind me and even though I am only 21 and have only had close to 7 years of driving experience I do have many miles under my belt doing these trips and have had no issues. If you pay attention to the road and what is going on around you and up ahead of you you can be a much safer driver even at higher speeds.
Not condoning it, but thats just my :2cents: