Why is it even possible? Because a car that can't do 100mph is going to have terrible performance 0-75
There's long stretches of highways in rural areas with speed limits higher than 75
>Not to mention, why are cars dumb machines? If someone is going crazy fast in an area where there is no safe way to decelerate, then the car should not allow that speed to be reached.
There are sometimes legitimate reasons to be going quickly. I have, at times, needed to have bursts of speed into the 90s to safely get around a drunk driver going 70.
You're now asking for cars to behave unpredictably based on their determination of the road conditions.
And you set the limiter to 75. Now someone is driving 75 in a 25.
Most highway deaths are rural[1] and involve a single car - they veer off of narrow lanes into a ditch or trees, or hit a large animal. The difference in reaction time needed to avoid said animals or other obstructions is not that different from 75mph to 90mph - low visibility is the underlying problem there, not speed.
The idea that we're suddenly safer on roads if we limit speeds is also not necessarily true.
In 2013, German autobahns accounted for 31% of the countries traffic, yet only 13% of the deaths. They had a rate of 1.9 deaths per billion kilometers travelled, while urban roads had 4.7, and rural roads 6.6.
I don't think there's really evidence to support the idea that limiting our cars to lower speeds will be beneficial.
[1] http://www.npr.org/2009/11/29/120716625/the-deadliest-roads-...