A higher average speed on the highway - pay attention now - leads to LOWER CONGESTION. It is a direct relationship. What gets people in accidents is primarily - you guessed it - CONGESTION. That is too many vehicles together, and too close by. This is true of the majority of vehicle accidents at speed.
When the speed limit went down, accidents increased. This was a major factor and has been identified as such in numerous studies. But insurance companies don't like the idea, and police want to have a reason to stop people whenever they want for whatever arbitrary reason they want... and there are careers with bonuses to think of...
It's been years since I last posted about it, but Texas, Italy, Germany and other countries have much higher speed limits for a reason - because studies and then practical experience have shown that the higher limits led to... that's right... lower congestion, which led to lower accident rates. There is also the attention factor - at a reasonable speed, the drivers' attention is on the road and not on other things, daydreaming, etc.