Yes, you need to double the speed and construct an artificial trafic burst to notice a marginal increase in capacity that is strictly due to the increased delay

Yes, you need to double the speed and construct an artificial trafic burst to notice a marginal increase in capacity that is strictly due to the increased delay (and storage capacity) of the slower road. That was my point. In practice trafic ramps up slow enough so that we can ignore the lost capacity due to empty roads in the early hours. After that, it is steady state for both scenarios. > there's plenty of other factors and practical road usage is nowhere near this perfect maximum of safe usage Precisely, but this even further argues against high speed limits. If the road tends to be congested, windy, has trafic lights and is poorly maintained, the areas where you can increase the speeds are very limited and the total impact in trip time is low. So high speeds not only not deliver higher throughputs but they fail to even deliver speed.