Pretty cool, by establishing a top speed standard they could run reliable crash tests for the absolute worst case that the car could experience. Looking forward to the future of "No matter how you drive this car, it won't kill you"
So speed is not the main issue but it's a nice tool when you're a politician or you want to communicate.
For the Autobahn, wiki says:
In 2014, autobahns carried 31% of motorized road traffic while accounting for 11% of Germany's traffic deaths. The autobahn fatality rate of 1.6 deaths per billion travel-kilometres compared favorably with the 4.6 rate on urban streets and 6.5 rate on rural roads.
Cars could still drive into lakes or off cliffs, but knowing the max speed a car could rear end another car may lead to minor enhancements that could save lives