In reply to toad:
its a tricky one - as folk have said, lots of vital shipments being made - 2 or 3 days of no deliveries and most supermarkets / shops would be struggling to fill the shelves and huge amounts of food wastage as it sits in depos.
Though I think a line should be drawn with red warnings (given how rare and normally short lived they are). Red = nothing leaves the depos, HGVs pull into nearest safe place for drivers to get accomodation. If it's forecast to stay the same for several days then include in resilience planning getting food etc distributed in the same way we do getting medical supplies out, vulnerable people moved around etc.
Where my folks live in south of France they do something like this that when the police declare "no travel" then HGVs are off the roads, full stop, no exceptions. This massively reduces the number of stuck vehicles, and so allows the plows etc to run unobstructed and so get and keep the roads open much more easily. Seems to work for them over there with a bit of foresight / planning. Anecdotal I know, but always worth looking at how other people tackle these problems and seeing if we can steal any good ideas!
It also takes all the pressure of drivers, so company can't push them to keep moving, and likewise the company shouldn't be under pressure from their clients as it's a police / national call.
A hard part would probably be making sure the drivers had safe and warm accommodation, food etc. given we don't have nearly the Aire / Service Station network they do in France to utilise!