There's no logic in many of our laws...
Someone behind a desk is justifying his job by pushing through solutions to problems that don't exist.
The 8 year old pillion one is just one example.
8 years isn't a magic number that somehow makes them capable. Kids are riding bicycles and mini bikes well before that age so they obviously have the mental capacity, it's not rocket science to be able to sit on the back of a motorcycle.
Another example, which was pushed through at the same time as the age limit one was the banning of transporting animals such as dogs etc on the tank of motorcycles. Was there an actual problem??? No...
Then there was the law they tried to introduce that would ban lane filtering/splitting, supposedly because it was so dangerous. It was only that it was worded so badly that it failed to be passed. As we all know now, it's now legal to filter pretty much Australia wide, amazing seeing as it was supposedly so dangerous not too many years back...lol.
Yet another which makes absolutely no sense to me is the requirement (in Queensland) to hold a car licence before you can get a motorcycle licence....cos driving is so similar to riding a bike...lol
Then of course there's the issues that West Aussie Glen & Bodø mentioned...
Perhaps I had better step down from my soapbox now...
