Utah tried this a couple of years ago on two stretches of I-15. The DOT and Highway Patrol have been collecting data. So far, there seems to be little effect on either the accident rate, fatality rate or how fast people drive. 85 seems to be some sort of mental barrier and is fast enough for most people, and folks don't seem to automatically set their cruise controls for 10 over the posted limit there.
Here, the change was prompted by a state legislator who lives in the southern part of Utah but frequently drives to the capital, SLC, in the north. Seems he wanted to decrease his travel time!
There are a lot of places in the western U.S. where there really isn't much of anything out there and destinations are long ways apart. Some studies found, back when speed limits were 55 and 65, many drivers fell asleep from boredom. Boredom seems to be less of a problem when you are driving really fast.
I have mixed thoughts on the matter. My primary concern is the increasing difference between the fast and the slow drivers on the same road that this will bring.
The last time I drove I-80 from Sacramento, CA to SLC, we stopped in Reno overnight. The next morning, east of there, with the light traffic, very good road, great weather and unlimited visibility, I set the cruise at eight mph over the limit. I didn't touch the brakes or the gas until we got to Wendover, probably 350-375 miles, and stopped for gas. During those several hours, I think maybe 6 or 8 cars passed me, and were not going much faster. It didn't seem terribly different from my normal, slower pace. I think people generally will arrive at a similar range of speeds they consider safe for the conditions.
Except for a few knuckleheads, of course.
