Michiganian here ... I've watched the speed limits increase over the last few years on all but residential roads and though my take is anecdotal, it's a fantastic thing as far as I'm concerned.

I used to drive 62 miles round trip to work, worked at home for a bit in between and am now back to about a 30 mile round-trip commute. Both were split equally on surface and freeway roads. Back when the speed limits were lower it was generally expected that most drivers -- during rush hour (assuming one could reach the speeds) -- would drive 50 MPH in a 40 and around 55 in a 50. It always surprised me -- every morning and evening on about a 6-mile stretch of road marked 40 MPH, there wasn't a car driving under 50 (and when that rare driver arrived, he was often tailgated so hard that traffic safety decreased considerably for him). Then, out of the blue, almost every road I took to work was changed to 50 MPH. Surprisingly, people weren't suddenly driving 60 MPH. I'm now on a similar commute as I was years ago, taking that same road, and people are consistently driving between 50 and 55 MPH on it.

I love our 85th percentile rule. It makes sense -- that one driver who's obeying the speed limit is being tail-gated by everyone else, reducing the distance between him and other cars, which increases accident probability and the relative severity of the accident since it will happen at a higher speed due to reduced braking time. When everyone is going about the same speed on the road, cars tend to be more spaced out and the relative difference in speed between the two objects colliding affects the severity of the accident.

There's also a lot of misconceptions about how speed is enforced -- at least in my area -- and what rules exist around speeding. I'm not sure if this is still the case, but it used to be that you were legally allowed to exceed the speed limit by 10 MPH on a freeway to overtake a vehicle in the passing lane. I have family who work in traffic patrol for the county and this topic comes up regularly. The department they work in encourages targeting people driving in excess of the speed of traffic, not folks who are keeping up with the speed of the cars around them. Of course, you can be pulled over in this scenario, and you are breaking the law[0], but at least in my area, it's not encouraged. An orderly system is safe, an outlier is unsafe, so they aim for folks who are driving in the left lane on a freeway in low traffic volumes, folks going over 20% of the speed of others and exceeding the speed limit, people jumping solid lines[1] and the huge problem caused by large numbers of people running red lights and failing to yield right-of-way when turning left[2].

[0] Both of them will tell you "If I want to pull you over, I can find a reason". A common one is those plastic covers/dealer advertisements around license plates or things hanging from a rear-view mirror. Some of the plate variations are legal (but there are very specific rules and almost all of them are not -- it's just rarely enforced), but most things hanging from the rear view mirror are obstructions.

[1] There are many places on the freeways in Michigan where the lane markers are solid white and for some reason, people don't understand that it's illegal to change lanes -- that's why they're solid. Aside from safety (they're put in due to increased blind-spots that make lane changes unsafe), they're often located in areas where people are entering the freeway and backups occur. Folks who panic at merging traffic or just don't want to slow down will jump lanes ... causing a worse backup.

[2] I realized this is going to sound uncommon to folks who don't live here, so pardon the long explanation. Easily the most common issue on road-ways in my area is people failing to yield when turning left at an intersection (my cousin/uncle will tell you this, but if you live here you're either already aware of the problem, or you aren't realizing you're doing it). Red light running is also more common here than in most of the country because of the frequency with which people encounter one-way intersections. It's legal, everywhere (except NYC and a probably a few other corner cases), to turn left on red when the road is one-way. Where I live, every road over three lanes (and many under) are engineered using the "Michigan Left" (https://en.wikipedia.org/wiki/Michigan_left). Often, though becoming less common, the "turnaround" is configured so that you can only turn left onto the same road heading in the opposite direction. Everything's fine when this is the case. However, it's grown popular to position these turnaround lanes in places that coincide with large retail business entrances or moderate traffic side-roads. All bets are off here. Because people are used to turning left on red in these turn-arounds, they assume they can also, legally, go straight into the side-road/business on red. Go ahead and google for signs telling people not to run red lights ... I couldn't find any. We have several of them on Hall Road in Macomb County. People are also used to "just going" when it's green, but you can't do that if the turnaround has traffic entering the road on the other side -- all of that traffic is turning right and has the right-of-way, just like in any other intersection -- left must yield unless they have a green arrow. I've been honked at on more than a few occasions by other drivers for not just plowing into the intersection, or not running the red to enter a side-street when traffic is clear but the light is red. Worse, once they put these hybrid side-street/turnarounds in, it destroys any advantage that the Michigan Left supposedly provides. It's already at a disadvantage since a portion of the traffic now has to pass through an intersection twice, but now the advantage of the "increased flow due to reduced traffic light phases" is overcome by the backups occurring in both turnarounds bleeding into a lane of traffic and the sudden pouring in of new traffic -- which has priority over existing traffic due to right-of-way -- entering in from popular businesses and busier side-streets (and, yes, a vein is popping out in my forehead now).