Driving in Tohoku may be a good way for getting to the remote spots but presents much of the same problems as driving in other parts of Japan, and then some: absence of proper signage (especially in English); inclement weather; following tour buses on narrow, winding, one-lane roads; and getting nearly run off the highways by big trucks driven by daredevils. Although gas, tolls, and car rentals make driving expensive, some areas, such as Hachiman-tai, are more enjoyable by car.
Most rental cars are equipped with a car navigation system (which is in Japanese but with English handbooks) so navigation may not be not as difficult as you would think. However, the speeds are limited to 80 kph to 100 kph on expressways, 30 kph to 40 kph on secondary roads and in urban areas, making travel considerably slower than the Shinkansen. The approximate driving times from Tokyo (assuming you can clear the metropolitan area in 2 hours) are 6 hours to Sendai, 8–10 hours to Morioka, and 10–11 hours to Aomori.
All major towns have car-rental agencies. Nippon Rent-A-Car is the one most frequently represented. Other car-rental companies include JR Eki, Toyota, and Nissan Rent-A-Car. These outfits usually have offices near major train stations, and even smaller ones. All you need is a valid International Driver's License (available from AAA in the United States) and your home state or country's license. Note that maps are not provided by car-rental agencies; be sure to obtain bilingual maps in Tokyo or Sendai.
Nippon Rent-A-Car (ニッポンレンタカー). ニッポンレンタカー 03/3485–7196; www.nipponrentacar.co.jp/english.
Toyota Rent-a-Car (トヨタレンタリース). トヨタレンタリース 0800/700–0815; 03/5954–8020; rent.toyota.co.jp/en/index.html.