change the law to ensure that road tax is used exclusively for roads

Roads in this country used to be world class. Now however after years of neglect and little money being spent on repairs they are an embarrassment making many roads akin to driving off-road.
Road tax was always explained as a means of financing road repairs but it has by successive governments been raided, leaving little or nothing left for the purpose that it was intended and leaving local authorities relying on government subsidies.