'Road tax' is just a confused generic term that stems from ancient history, when the 'Road Fund' was hypothecated to pay for roads. For some reason, the 'road' component has stuck. It's incredibly difficult to dislodge an urban myth once it's taken hold in English. If you have to explain it on the street, just simply say something like: 'There are several reasons why you have to pay tax on your vehicle but I don't have to pay tax on mine. There is no tax on roads.'
[ame]http://en.wikipedia.org/wiki/Vehicle_excise_duty[/ame]
'Road tax' is just a confused generic term that stems from ancient history, when the 'Road Fund' was hypothecated to pay for roads. For some reason, the 'road' component has stuck. It's incredibly difficult to dislodge an urban myth once it's taken hold in English. If you have to explain it on the street, just simply say something like: 'There are several reasons why you have to pay tax on your vehicle but I don't have to pay tax on mine. There is no tax on roads.'