A person who doesn't drive
still makes use of the roads.
He may use buses or taxis.
He may even use a bicycle.
He may order things to be shipped to his home or work by truck.
Goods he buys/uses in supermarkets, hardware stores, barbershops, etc. all can be delivered by car or truck.
His police, fire, and ambulance services all use the roads, and it is better for them and you if the roads are maintained in good condition.
He also is likely to have his mail delivered by a road vehicle.
Also, you can't really impose separate road taxes, can you? Tax is tax, and how the governments decide to divide it for various uses is up to them.
Goldiegirl,
Your husband probably has an ETC account, which permits faster passage through tollgates here. You should ask him how much he pays per month.
According to this forum report, the cost for tollway use (which probably varies according to prefecture, IMO) is 24.6 yen/km for cars and 19.69 yen/km for motorcycles and light vehicles.
http://www.japan-guide.com/forum/quereadisplay.html?0+11712
The forum discussion also brings up this Japanese site.
年会費無料で選ぶおすすめETCカード|一番お得で便利なETCカードを徹底比較|クレコミ|クレジットカードの口コミ比較情報サイト
Wikipedia has this to say about tolls on expressways, too, with a nice table of how much it costs per km or mile depending on which type of vehicle you use.
According to Wikipedia
toll collecting companies are private, supposedly "to encourage competition and decrease tolls".
Transport in Japan - Wikipedia
But the other Wiki link above shows who owns which expressways.