I usually agree with the gravel road = street theory, as many are well maintained, easily fit 2 cars abreast & you can travel at reasonably high speed. I like the way you've addressed this one though as it was much narrower, and traction was a problem. Don't know if my GPS track shows or not but I doubt I got over 50km/h!

I'm not disagreeing with that, just saying that on that particular stretch I might not have got to 50km/h at all, let alone averaged it.

so I have left either end where it joins the main road with a street rating for a few hundred meters, then changed it to the dirt track for the middle portion of the road. This means it will show on the map when you are driving along SH2 and also at the other end

Good solution - it makes the road visible where it intersects yet unroutable for general use, unless of course your destination is on that road