I live in one of the worse states for speed limit setting and enforcement. In Ohio, the speed limit is way low (sometimes illegal for the road to be defined as an interstate) and there is massive enforcement. You see cops everywhere sitting in the middle of the road, idling, waiting to catch a random speeder.
There are some major problems with keeping the highway limit too low: First, interstates are much better able to handle large amounts of traffic. That can't be denied. Very large radius turns and very long sight-distances with many other measures to handle large volume and to be able to see far in advance what is going on. Second, most people will always try to find the fastest way to get somewhere. Now here comes the big issue. Lowering the limit on the highway (like they did with the 55 mess) pushes a large volume of traffic onto secondary and county roads. It's very easy to do 55-60 on a lot of lonely stretches of county & township roads. Except they don't become so lonely anymore. The death rate soars on these side roads people use to try and beat the highway. Very rarely will you see that listed in statistics. Advocates for lower speeds tend to focus on just the highway death rate even though the overall deaths/mile is increasing. Which makes complete sense, because you want the largest volume on the safer highways.
Here in Ohio, trucks are still limited to 55 mph. Whereas car traffic can go up to 65. We will stay away from why that is so silly to increase car to truck interaction with the speed differential... but this phenomenon was still happening with the trucks! They were jumping off the highway and trying to fly through small towns. These trucks were slamming into minivans and killing people left and right. They finally relented and let trucks do 65 only on the turnpike, state highway patrol (speed increases biggest opponent in Ohio) was coming out with reports of fractional increases in total accidents on the turnpike within weeks. Of course with nothing stated about how many involved trucks.
I can understand why many people on here think everyone should just go slow, unfortunately its not going to happen en masse anytime soon. But in the meantime I think the safety factor should also be considered in setting speed limits, too. I can't imagine justifying people dying for FE reasons. Let the people live and educate them on why they should drive slower.
I know I am enjoying the learning.