by ryao | 2025-04-28 19:25:06+00:00
> Seriously. That is a pretty bold claim that you should be able support with actual studies, if true

The 85th percentile rule/principle has been understood for decades. Just search for information on it. You will find tons of results. Calling it a bold claim is like claiming asymptotic complexity is a bold claim. It is something that is well known, just not to you.

> It has been proven in both theoretical and practical tests that driving "all out" does not decrease travel time drastically in almost all circumstances.

Those tests do not seem relevant to highways, where it is easy to measure differences in travel time between driving at the speed of traffic and driving at the speed limit. When traffic is at 70mph and the speed limit is 55mph, keeping pace with traffic results in a 21% reduction in highway travel time. How things go when someone is ‘driving "all out"’ is not relevant here.

> Forcing people to drive slower drastically reduced the risk of collisions because people are slower and have more time to react.

A highway is not a regular road where it is stop and go based on lights. The purpose of a highway is to have a free flow of traffic such that you do not need to be continuously reacting to others. You do need to maintain a certain distance between you and the car to react in emergencies, but these are supposed to be exceptional and plenty of collisions occur when changing lanes, which would be lessened with fewer cars on the road. Cases where everyone needs to stop would also be lessened.

> You'll have to control for other factors, of course. Cars in the US are much larger and heavier than in Germany, for example. In statistics, you want to compare apples to apples, so you control for vehicle weight when trying to make observations about the impact of speed on accident severity.

Those same vehicles are legal to drive in Germany as far as I know. There is a possibility that they are popular in the U.S. because of the speed limits such that they would be less popular if the highways did not have speed limits. After all, their acceleration, braking and fuel economy are terrible. They would only be worse at autobahn speeds. The knowledge that it is legal to drive at higher speeds tends to encourage people purchasing vehicles to purchase ones that can handle higher speeds well. We could see vehicles more similar to those driven in Germany become popular if there were no speed limits and then things would naturally become apples to apples.

> True. But the same holds true for vehicle collisions. It's really basic physics. All other things being equal, faster cars have more energy. More energy = more severe accident outcomes.

There is no law of physics that dictates that such things cannot be done with greater safety than we currently have. Germany is a fantastic example of this. Germany permits speeds that would be considered hazardous by the thinking behind motor vehicle rules in the US, yet is substantially safer.

> No. There are plenty of other sources that support my views, i.e.

If I tell you what is wrong with your sources one last time, I hope you will stop posting links under the misguided hope that some random thing superficially agrees with your claims sticks. Your first link involved studies in a country where speed limits should obey the 85th percentile. The findings are not relevant to the U.S. where the 85th percentile is ignored. Even without knowing about the 85th percentile, it is obvious the applicability to other countries would depend on how similar the process for establishing the speed limit is. Your second link is behind a paywall and cannot be scrutinized, but the German autobahn likely contradicts it. Problems only occur when the distance between a vehicle and another object reaches 0. If that is avoided, the speed does not matter.

That said, it is impossible to prevent future Darwin Award recipients from earning their awards. If you insist on trying to stop them from earning rewards from motor vehicles, you might as well push for a complete ban on motor vehicles. That is the only thing that would eliminate motor vehicle fatalities.