How Do We Decide Speed Limits?

We know speed limits exist to prevent speeding related car accidents, but how exactly are they chosen?

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Long-Term Effects of Repealing the National Maximum Speed Limit in the United States (NCBI)
"We examined the long-term effects of the 1995 repeal of federal speed limit controls on road fatalities and injuries in fatal crashes. We used a Poisson mixed-regression model to assess changes in the number of fatalities and injuries in fatal crashes between 1995 and 2005 on rural interstates, where all US states have raised speed limits since the repeal, as well as on urban interstates and noninterstate roads, where many states have raised speed limits"

Traffic Safety Facts: Speeding (NHTSA)
"NHTSA considers a crash to be speeding-related if the driver was charged with a speeding-related offense or if a police officer indicated that racing, driving too fast for conditions, or exceeding the posted speed limit was a contributing factor in the crash."

Methods and Practices for Setting Speed Limits (FHWA)
"This report presents the various procedures that highway agencies can and do use to set speed limits. It is an informational report and provides a broad overview of the different speed limit setting methods that are available, but makes no specific recommendations or suggestions."