I'm all for raising speed limits, but there are sometimes where speed limits are just fine where they are. If anybody here is familiar with I-44 north of Rolla, the speed limit of 70MPH is just fine where it is, but after I-70 is upgraded to a straight shot all the way from STL to KC, something around 85MPH could be possible. The only problem is that people in MO don't like passing in the left lane but instead sitting in the left lane going 65MPH trying to save the environment or something crazy like that.
You can have speed limits at 100MPH but there will always be: trucks, slower cars (those cars that are held together with duck tape, you know what I mean), and inexperienced drivers. If you want to have higher speed limits and safer roads, we need to raise the standards of our cars allowed on the roads and the drivers themselves. In my opinion, DUI and texting-while-driving should be very serious offenses and should send your license to the shredder. It's just too dangerous. It would be nice if semi-trucks could go faster, but they can't. And really if we want to make speed limits much higher, we need to rebuild many of our major freight corridors. Because trucks can only do so much, and they are very dangerous when going very fast (90MPH? I really can't give you a number here.)
If we in the US want to have German Autobahn speed limits, you need a 6 lane road. There's too much going on to fit in 4 lanes. Personal opinion.