mate that is the scenario for criminal offences and trials. but these sorts of matters are ones of administration - think immigration, customs etc - where the government bodies (ie. vicroads) are given broad powers to, say, check your exhaust dB levels to make sure they comply with regulations in the interests of the greater community.
don't get me wrong i think it's taken a bit too far myself, but i'm just telling you how it is. and before you ask, yes there are mechanisms in place to keep these authorities in check - how effective they are is another matter altogether.
oh and in case you were wondering, i have studied this sort of thing before.
Ric