road tax A vehicle- owner pays an annual tax, broadly reflecting the vehicle’s use of road space, the road wear it causes, and the need for social equity. Specifically, for cars and motorcycles, the tax is based on engine capacity; for goods vehicles and buses, it is based on the maximum laden weight and number of axles. For vehicles more than ten years old, the tax increases at the rate of 10 per cent (of the basic road tax payable) per annum from the 11th year to a maximum of 50 per cent in the 15th year.