Speed difference is also an issue. Speed certainly kills.

Increased speed limits in BC increased fatalities: https://www.cbc.ca/news/canada/british-columbia/fatal-crashe...

Road Safety Impact of Increased Rural Highway Speed Limits in British Columbia, Canada https://www.mdpi.com/2071-1050/10/10/3555/htm sustainability-10-03555-v2.pdf

https://icsw.nhtsa.gov/nhtsa/fars/speeding_data_visualizatio... 27% of fatalities were speeding-related

“There is a great deal of evidence that if you drive just two percent faster, your risk of being killed increases by 10 percent,” https://www.autoblog.com/2010/06/23/speeding-health-hazards/

Moreover, traffic flow is worse at higher speeds, and there's more pollution, and it's louder. And we have to spend more money on roads.

If one were to want to drive fast, the best place would be a race track.

The issue with ground based traffic is that you have a lot of non-moving objects around you, like trees, walls, animals, etc. So even if all cars drive at 250 km/h, those non-moving objects still remain there and pose an ever increasing risk with increased speed. Furthermore, curves are more dangerous at higher speeds.

We’re talking about the Autobahn, not a random road in the forest or a city. Those are designed for the speed.

Due to topography, Autobahn roads can still be very curvy. The Albaufstieg [0] is an extreme example but not the only one. Notice the sign at 3:04, it's limited to 60 kmh. Weather can make those curves even more dangerous, e.g. rain or ice. As for objects, they still occur. One example is prior accidents. Another example is the end of a traffic jam. These are an especially bad problem for trucks [1], that actually drive way slower than 130 kmh even. The problem here is driver attention, but too fast speed can also contribute [2].

[0]: https://www.youtube.com/watch?v=IBbAvzXhwNQ

[1]: https://autofahrerseite.eu/sicherheit/524-lkw-unfall-stauend...

[2]: https://bz-ticket.de/massenkarambolage-auf-der-a5-kettenreak...

I know that A8 part. It’s pretty cool. The speed limit there is most likely due to how steep it is. Trucks are pretty slow there. The ICE goes around that mountain as slow as the traffic on the Autobahn.

Ok, so you are saying that more problematic road parts have (and should have) lower speed limits.

The higher your speed, the higher your speed differential with the road and guard rail. A car nudging another at 250 km/h can cause the other to violently roll over, while a car nudging another at 40 km/hr can't. Speed differential between cars is not the only factor in safety.

I agree, and if we had decided to create an autonomous car only line where the speed gets controlled by a central computer, this would apply. You still shouldn't ignore that the higher the speed, the more likely larger speed differences can appear. At some point external force will slow down cars significantly faster than the brake of the vehicle behind.

Trucks are only allowed to go at 100km/h at the highway in Germany and are therefore a major obstacle for the car drivers going at much higher speed.