Snow & Public Transport

In England anything above 1mm of snow pretty much shuts the country down. I would assume that Norway is a little bit more experienced at handling it.

I'm sure that Oslo gets plenty of snow but does anybody know how it typically affects public transport and traffic in general?

Should I plan for extra journey time or will it be business as usual?

It was a particularly harsh winter last year, much more snow than usual.  I can't speak for Oslo, but in Bergen it was pretty much just "business as usual".  Maybe it took a little extra time if it was actually snowing whilst on the bus, but not much.