Hi Luke (and Arno -
I passed the question on to a Swiss friend who is active in hiking and travel throughout Switzerland in all seasons. He is not a cyclist.
Here is his reply, in two parts-
<<"He won’t meet -30°C temperatures in the Alps, at places where there are roads. He will find opportunities to refill his water bottles after having used less than two liters. If he doesn’t want to cycle on high traffic roads, and at the same time wants to do his cycling in the winter, he is running into a contradiction: the few roads that are open are used by trucks and buisses essential to bring food, fuel, school pupils etc. to the last village of remote valleys. On the other hand, if he did his trip between May and November he would have access to small mountain passes, still paved, or maybe unpaved, but with almost no trafic (such as the Sanetsch between Bern and Valais).
So much for good advice. Now, great inventions and discoveries were made by unreasonable people who did not listen to good advice! So:
A list of the Swiss mountain pass roads, their max. slope and whether opened or closed, if so when, can be found on the web pages of the TCS (=Swiss AA). Available in the three Swiss languages, not English, but it is fairly easy to figure out the months names. That’s here:
I have noted on the pass list in your message the finding on Swiss passes, most are open throughout the year. Of course this is an indication only, the police makes decisions based on the actual weather conditions. Sometimes they close the road at the announced time in spite of there being no snow, to carry out road maintenance jobs. I would strongly advice not to go on closed roads, the avalanche protection structures on roads are insufficient to protect against winter avalanches. If you break that rule, at least don’t go alone.
From my motorbike days I know some of the passes in the other countries. No idea about they being open or closed in the winter. I suppose the Reschen Pass (Austria/Italy), which is at a low elevation, would be open throughout the year.">>
<<"He can also check out the site of MeteoSwiss:
Also available in English. I suppose that « Slippery Roads » could be useful, but only for short-term information (up to one week). As right now there is no slippery road in all Switzerland, it does not look impressive. MeteoSwiss also has an app for smartphones. Very useful, and rather accurate.">>
Arno- I am recalling my drives through mountain tunnels on the traverses of the passes in the winter (or other seasons). If they are long they stink from exhaust fumes , and have no special provisions for cyclists, if I recall correctly.
I suppose that bicycles have the same status as automobiles on those roads, but I'd not want to be in one of the long uphill tunnels.