Where To Drive and Where Not To
Where are the best places to drive in Japan? Well it depends on what you are looking for, but in my opinion the further north you get from Tokyo the better the driving is. While I haven't driven everywhere I have driven quite a bit in Tohoku, Kanto, and some of Kansai. For a general idea of where the best driving is you can look at a population density map. The more dense the population the worse the driving will be. That means that the areas around Tokyo are not the best to drive in, but it's not at all impossible.
Wherever possible you want to try to avoid large cities unless you are specifically going to them. The reason for this is that the traffic through cities moves slowly. There are few highways or by-passes and most of the traffic has to funnel through the tangle of streets in downtown areas. Around Tokyo you can expect to move on average of 10-15km per hour. Also, the area between Tokyo and Osaka contains a significant protion of the Japanese population and is basically a continuous city and can be slow going even on the highway. Tokyo to around Sendai or Morioka, following the highway (and shinkansen) in the center of the island, is also dense, but much less so than the areas around Tokyo.
So where do you recommend driving then? The answer is around the edges of the islands with occasional exceptions. My favorite place to drive so far is along the pacific coast north of Sendai. Starting from Matsushima, supposedly one of the three most scenic places in Japan, the road along the coast is quite scenic and dotted with little fishing villages. There are generally no or few trucks and there are lots of chances to experience little onsen, great local restaurants, and meet interesting people. This area is also very difficult to get to without a car so there are few tourists. Going north and inland a little bit, Tono is worth a visit. Once you get past the main drag of pachinko parlors and car dealers the old town is VERY quant and picturesque (watch out for those rice farmers on the road - the drive like maniacs). The drive from Tono to Morioka is also quite pleasant, but once you get down out of the mountains and into Morioka it is less so. The center of Morioka has a nice castle ruin and good local crafts, but it is a city with all the city driving fun that comes with it (but not nearly as bad as Tokyo).
Another good area to drive is north of Hachinohe (final stop on the Tohoku Shinkansen) and around the Shimokita-hanto, the ax-shaped peninsula to the northeast of Aomori. It is quite stunning and, in my opinion, offers some of the best traditional northern Japanese culture anywhere, and is almost completely inaccessible by public transportation. Osore-zan and the yayagen valley are particularly nice to drive around (don't miss the kappa pools onsen). The area around lake Towada is also very nice, but it can get quite crowded during the summer and fall.
While I have not personally driven in Hokkaido many people say that it offers some of the best driving in Japan (in the summer). They say the roads and countryside are like America. The roads are long and straight and they don't have very many people on them, but people drive very fast. Also, the Japan Sea coast north of Niigata is said to be nice.
There are some nice areas to drive in the Kanto region, but they are not as nice as Tohoku. The drive around the perimeter of the Boso peninsula in Chiba prefecture is nice and there are several unique attractions. Starting and ending in Chiba City it takes about 8 hours to drive around the entire peninsula. Also, the area around Nikko, Nikko National Park, and lake Chuzenji is very nice and features several spectacular waterfalls. It is possible to see the best of Nikko area by train and bus, but you are, of course, more flexible with a car. Mashiko, a small pottery town north of Tokyo and east of Utsunomiya (and Nikko), is also nice to drive around. It is possible, but difficult, to get to Mashiko by train.
I don't have a lot of experience driving in other places in Japan, but I'm sure there are MANY more great places to go driving. I suspect that the entire Sea of Japan cost would be nice to drive along as well as Shikoku and parts of Kyushu. If you have ANY ideas on nice places to drive in Japan PLEASE leave feedback and let me know!
I hope this article has been helpful for anyone planning on driving in Japan. Please let me know what you think of it on the feedback page.