The following is a post I made in reply to a posts on another forum.
I thought it was suitable a subject for a general good natured 'discussion'.

Are vehicle manufacturers towing speed restrictions etc legally enforceable?

It remains a "Grey Area' in law as to whether there is a legal requirement to tow at the lower speeds recommended by some manufacturers and also if a WDH is also a legal requirement if quoted by the vehicle manufacturer.
I wrote to Vicroads more than 4 years ago raising these questions in relation the Holdens requirements.
Their reply was to send me a photostat of the page from a Holden handbook with the paragraphs highlighted without explanation.
I then forward their reply to the Victorian Justice Department with the same request, and their reply was to quote the Vicroads reply to me.
I ran my original letters and the replies past my Solicitor when I was there on company business and asked him for an opinion.
His opinion was that as neither Department was willing to make a factual statement or place my query before the Road Safety Committee for review that they didn't think the request merited any further consideration.
In those circumstances the matter would have to be tested before a court. i.e. If charged with exceeding the speed limit while towing or not using a WDH, the authority laying the charge(s) would first have to actually find the correct charge to lay.
They could then issue an infringement notice which you could fight in court. The magistrate would then have to hand down a decision and thus set a president one way or another for future such infringements.
This determination would stand unless overturned by a higher court.
According to the Solicitor these fall into the same "Grey Areas" as driving in smoke.
E.g. When driving in smoke are you required to put your headlights on?
The law requires headlight to be on between sunset and sunrise and anytime weather conditions reduce visibility. i.e. Rain fog etc.
Note: Headlights, not parking lights.
There is no reference to smoke over the road in the road traffic legislation.
It could be argued that smoke is not weather an so having headlights on is not mandatory.
It could equally be argued that the weather conditions i.e. the wind, caused the smoke to be over the road, and thus, having headlights on is therefore mandatory.
As you can see. Lots of unanswered things crop up all the time that require a court ruling. I really don't think to many cops or RTA officers are going to go down that road with all the paperwork involved and the possibility of loosing.
Hope you all had a great Easter all, and were quick enough to beat the kids to all the choc eggs.
Cheers, ozjohn.

Replys from another forum have turned up the following:
A Magistrate can't set a precedent only make a ruling which could be overturned on appeal.
SA legislation cover smoke over the road as it refers to reduced visablity.

I can't find anything in the my search of the NSW RTA or Vicroads sites that have similar wording only where weather reduces visbility.

Cheers, ozjohn.