Snailway rhymes with Railway. That's why I thought you were talking about trains.
The speed limits are probably mostly there for the winters. There's about 3 hours where you are either driving through mountains or river canyons that are at least half a mile deep (probably closer to a mile). The other half the time, you are driving on rather flat surfaces with no trees where if there is snow on the ground and the sun is out (common occurrence in winter), it quickly becomes blinding.
Not to mention the whole road is a giant deer crossing, and you don't want to hit one of those going 100 mph.