A lot of people drive faster than the posted speed limit - 75 to 80 instead of 70. Increasing the speed limit will just push the actual travel rates higher - 80 to 85 instead of 75. With all of the heavy trucks on the road (some that drive slow), higher speeds are just dangerous.

Drivers are already driving 5 to 10 miles over the current limits so if it's increased I'm pretty sure they'll exceed the new limits.