Snowy Alpine passes

[foxyrider]

Does that mean winter tyres OR snow chains?

--> YES

What about four-season motor tyres, or spiked cycle tyres?

--> both acceptable I guess

Vocab: can't circulate = may not proceed

--> i think you are formally forbidden to circulate, nevertheless, in absence of any police control you may proceed, though at your onw risk and under your own complete responsability.
I never experienced anything like that with my bicycle but with the car, under snow conditions, police stopped me twice and checked for chains available on board, nobody however checked whether chains where the ones correct for that specific car!!

Never heard of chains being for specific cars - the ones we have are adjustable to fit and would fit most family cars without issue. They are however a bugger to fit on anything.

With the adoption of disc brakes shouldn't it be possible to have some sort of 'chain' or wrap for bikes instead of having to change tyres?

[ConRAD]

... chains out of the shelf are afaik adjustable to fit car tyre sizes within a certain range but they are definitely not "universal" at all, also their thickness might be sometimes an issue expecially when distance between tyre shoulders and car chassis is very limited.
... for bicycles i've never seen "chains" but only snow/ice nailed specific tyres

[foxyrider]

Alpine rides completed.

1 failure - started snowing @ 700m asl, turned back as road was covered.

2 low passes, no problem

1 slightly dodgy - icy road @ same height although the day was sunny and almost into plus,

1 very cold success - 1400+m with snow around, bit dodgy on damp downhills with potential ice.

Conclusion

It's quite doable provided you are sensible. Snow/ice tyres might give a bit more peace of mind for descents - I managed on 25c Paselas but there were times when they felt a bit sketchy on the frozen downhills. Even the little bit of snow I did encounter on the roads very quickly collected on the bike - and froze so that the gearing was all over the place.

Advice

Remember the rain at lower levels could be snow as you climb.
Always have a plan B, no shame in aborting if the weather closes in.
Tell someone where you are going with an eta - check in with them if you are delayed.
Dress warmly

If anyone wants more specifics just ask

[Cyril Haearn]

State of emergency in German and Austrian Alps now, 4m snow fell in a few days, more snow falling, several villages cut off
Could last weeks or months

[foxyrider]

State of emergency in German and Austrian Alps now, 4m snow fell in a few days, more snow falling, several villages cut off
Could last weeks or months

Timing is everything, Lech where the skiers were killed is only a few kilometres from where I was on Boxing day. Whilst it might look very pretty it is dangerous, 3m of snow on a roof can cause it to fail, that's happened in the past, the authorities seem to be concentrating on at risk buildings as much as clearing roads.

As I said before, No.1 priority should be for your own safety, if it looks dodgy turn back. That applies even in less extreme locales.