At the heart of the current argument over whether or not to continue the special gasoline tax is a question that gets overlooked: Does the central government have too much control over prefectural governments?
Prefectures rely heavily on central-government money to run their operations and fund public works, and matters involving education and security are completely decided in Tokyo.
Occasionally, you will hear talk about the need to give prefectures more autonomy, but this isn't practical. Perhaps if areas were fused — the four prefectures of Shikoku, say, or the four that make up the Tokai region — you could form constituencies large enough so that local governments could raise more tax revenues by themselves and pay for their own road construction. As it stands, most prefectures are too small to accomplish that on their own.