This is just a part of the E61 road, which connects Italy, Slovenia and Croatia but continues beyond.
We took it to complete the tour of Istria and return to Trieste, and it was an excellent choice:
1) good asphalt and not too steep slopes, even if it is a continuous up and down
2) in the morning, in the middle of summer, it was cool because almost all in the woods. At these times it was not even too busy, especially returning to Italy
3) the views are wonderful, with typical karst woods, coniferous plateaus, avenues of lime trees and much more.
4) every now and then there are rest areas and trattorias in some towns, to stop and eat something
It is not a road that everyone would appreciate, due to the traffic and the effort of the climb, but a cycle tourist with a bit of experience will almost certainly find it splendid.