The roads are very smooth and clean, but this means nothing when you are restricted to drive 30kmh most of the time. Yes on an average trip, my estimated average speed in Japan is around 25-35kmh. So a trip that is 70km away, is sure to take longer than 2 hours. There are many reasons for this:
Motorways are very limited in numbers and have a maximum speed of 60kmh (most common) or 80kmh, and there is a strict speed control via cameras and patrol cars. Dual carriage-ways that are not motorways have a speed limit of 50kmh, and are controlled by traffic lights for every junction (every 500meters on the one that I use most often). The most common single carriage-way roads have a speed limit of 40kmh and they are controlled by traffic light that are upto every 200m in frequency. The existence of uncontrolled junctions or roundabouts has been obliterated from Japan (because they must be unsafe). On top of all this, the traffic lights have no sensor control, and they are on 24hrs/day.
I remember a discussion by a group of lads at the army about the "need" to have a motorway from Lefkosa to Magusa (the two major cities in N. Cyprus). They were complaining that with the current dual-carriage-way road it took around 45minutes to travel between those two cities (of approximately 65km). I wish them a year of driving in Japan with a fully modded racing car.