Can anyone tell us about the condition of the hiway between Bovec and Kransjska Gora? About how long a drive is it? We have driven plenty of crazy switchback roads in Norway. What's it like?
I haven't been on that road, but ViaMichelin says the trip is about 27 miles and will take about 52 minutes, so don't expect a straight highway. You can zoom in on the map and see that parts of the drive will fall in the "interesting" category, if not "hair-raising".
I am assuming you are referring to the Vrsic Pass (road 206, the first option on acraven's link), the "drive through the Julian Alps" that is described in most guidebooks. The road is two-laned all the way, comfortable enough in the valley, a bit narrower on the mountain pass, but always wide enough for two cars to pass. This is what it looks like in the narrower section (per Google Street View): https://email@example.com,13.7454085,3a,75y,157.93h,82.31t/data=!3m6!1e1!3m4!1sKjRXqV2kgo75EUdQLbAccQ!2e0!7i13312!8i6656
It takes about an hour to do the drive, but with stops at lookout points, monuments and at the summit, expect the drive to take closer to two hours. If you want to do shorter hikes from the road, plan for longer - for example, hiking the Soca Trail along the Great Soca Gorge (1 hr), to the source of the Soca River (30 mins - 1 hr), or a hike from the summit to the incredibly scenic Slemenova Spica (3 hrs), etc.