Hi,
The "problem" with this road is that it goes through a military zone and is only open to the public during certain times. Any other times access to the area is closed and artillery fire has to be expected. Guards are on duty. Each year the road is officially closed November 1st to May 31st http://hongrin.ch/ As far as I understand this includes any kind of traffic. It is also closed to any kind of traffic on weekdays if shooting exercises are held as published here: https://www.vtg.admin.ch/de/aktuell/mitteilungen/schiessanzeigen.zensa_detail.html/1201.050.html
On weekends it is usually open ("Bürozeiten" ;-) If you know what I mean.)