If there was a European-wide competition for the least intuitive method of toll collection, Norway would win the prize. So, if you plan on driving a car in Norway without doing much prior research (as I foolishly did today), don't let their toll system surprise you. To describe, I was driving towards Trondheim and I saw a sign that read something like "Automatic Toll collection, 5 km". I assumed this would be similar to the EZpass system used in the US, and that you would have the option of paying at a booth. Well, after fishing through my pocket for the correct amount of kroner, 5 km had passed and I didn't see a booth. Hmmm, that was strange. About 15 km later, I saw an additional sign announcing another automatic toll collection. Once again... I drove along and didn't see a booth. I took the same route back, and this time I noticed the sensors that spanned over the road. OK, so they're obviously noting each vehicle as it passes, but how the hell do I pay? A little after-the-fact online research revealed that you either have to pre-register your vehicle online and buy credits, or you can leave the motorway immediately after passing the toll point and pay at a petrol station. If you do neither, you will receive a bill in the mail at a later time... which, I assume, I will... I doubt Norway is actively trying to entrap unsuspecting foreign drivers, because being particularly isolated from the rest of Europe, foreign drivers probably constitute a tiny minority of those on the roads (unlike Germany, whose roads seem to be clogged with the motorists of every country in Europe!).
Tom, They do indeed mail the toll, plus some reasonable administrative charge (it's less than € 10 for each month's bill), to other countries in Europe. Here in The Netherlands it takes around 5 weeks after the calendar month in which you traveled ends before an invoice is received. I guess they have many lightly trafficked toll roads/bridges with even fewer international non-Swedish traffic, so they just just this system.