In the UK it was originally based on something like the 85th percentile: the speed most drivers would normally pick for the road given no imposed limit.
These days it’s more based around what politicians live where, so we have dual carriageways with central reservations, which would normally be 70mph, but because some fancy nob has a house there and doesn’t like noise, it’s got to be 40mph. They don’t say that though, they say it’s down to too many accidents in the area, or speed reduction for air quality or some other nonsense (if it was for air quality then the limit’d be 60mph due to the designed-in peak efficiency at 55mph).
In the UK it was originally based on something like the 85th percentile: the speed most drivers would normally pick for the road given no imposed limit.
These days it’s more based around what politicians live where, so we have dual carriageways with central reservations, which would normally be 70mph, but because some fancy nob has a house there and doesn’t like noise, it’s got to be 40mph. They don’t say that though, they say it’s down to too many accidents in the area, or speed reduction for air quality or some other nonsense (if it was for air quality then the limit’d be 60mph due to the designed-in peak efficiency at 55mph).