I have seen truckers turn there flashers on for years when they are moving slow entering the freeway or pulling away from a stop all over the country. If you've ever driving in the mountains this is common practice going up steep grades when there speed drops below the rest of traffic.
As far in bad weather snow or rain the best thing is not get caught in it but if you have to slow below minimum speeds than best thing is either get off the highway at the next exit or not as safe as exiting is pull way off the side of the road is possible.