The US interstate speed limits are at most 120 kph (75 mph) and are 105 kph on average (65 mph), and can be as low as 90 kph (55 mph), so that's almost certainly what Tesla bases their "highway" estimates off of.
160 kph+ (100 mph+) is way past the efficiency sweet spot :)
US interstate speed limits have their roots in fuel conservation for WW2 (or noise control in wealthier spots), safety was just a side effect at least at first.
I've lived in a few different states across the US and I've yet to happen across one. (I am an American, yes we all learn metric in school, you can blame Reagan canning the attempt to switch in the 80s)
160 kph+ (100 mph+) is way past the efficiency sweet spot :)
US interstate speed limits have their roots in fuel conservation for WW2 (or noise control in wealthier spots), safety was just a side effect at least at first.