This question relates to
… the maximum speed at which a trailer can be towed under response conditions SES GLR accredited unit (rule 306). For the purpose of the argument let’s assume that we have level 3 swift water technicians responding to persons trapped by rising floodwater,
The driver is a NSW SES level 3 approved driver (lights & sirens) they are towing a boat on a boat trailer.
At what speed should they respond? One piece of advice that has been obtained is not exceeding the “rated” speed of the trailer, (no rated speed displayed on trailer, possibly contact maker).
Also a similar situation could arise with a vertical rescue unit towing a trailer (with VR gear inside) responding to a call same driver authorisation as the above example.
The reference to rule 306 is a reference to the Road Rules 2014 (NSW) r 306. This is not a blanket exemption from everything to do with driving. It is an exemption, to the extent it is an exemption at all, from the other rules listed in the Road Rules 2014 (NSW) and not all the rules relating to driving and vehicles are in the Road Rules 2014. The Road Rules do contain provisions about towing cars or motorcycles (see for example r 294-3 NSW rule: towing restrictions generally) as well as some provisions about towing trailers. For example r 294-2 provides that a driver must not tow a trailer or other vehicle
… if the laden weight of the towed vehicle exceeds:
(a) the capacity of the towing attachment fitted to the towing vehicle, or
(b) the maximum laden weight for the towed vehicle.
That says nothing about ‘speed’.
Regulation 21 provides that the maximum speed for a ‘vehicle and trailer combination with a GCM [Gross Combination Mass] over 4.5 tonnes … is 100 kilometres per hour’. That appears to be the only relevant speed limit in NSW (see also Road and Maritime Services, Towing (u.d)).
Discussion
If there is a rated speed of the trailer then of course you should not exceed that speed. Remember that the most important road rule is don’t crash and don’t kill anyone. If there is are ‘persons trapped by rising floodwater’ saving their lives does not justify killing someone else. And if you crash you’re not going to get there to save their life anyway. If the trailer has a ‘safe’ speed, exceeding that speed, even if you are lawfully entitled to, would not be exercising ‘reasonable care’. So if the rated speed of the trailer is 80km/h and the speed limit is 100km/h, you don’t need r 306 to travel at 100km/h but you are not taking reasonable care. If the rated speed for the trailer is 100km/h and the speed limit is 100km/h, r 306 won’t justify travelling at 110km/h as again you are failing to take ‘reasonable care’.
Remember this case from Victoria – Suspended Jail Sentence for Firefighter Involved in a Fatal Accident (October 24, 2009). There the driver was travelling under the prescribed speed limit but, according to the sentencing judge, ‘there was an “inescapable inference’’ that [the driver], who knew the truck was top-heavy when filled with water, was driving it ‘‘just too fast’’.
In the context of the question I am considering if the weight, load distribution and recommendations of the trailer and vehicle manufacturer suggest a particular maximum speed then travelling over that speed is ‘just too fast’ regardless of the posted speed limit on the road, or the needs of the people to whom you are responding.
Conclusion
Rule 306 gives some exemptions from the road rules but only when it is safe to do so. The speed at which you should tow a trailer is a matter of safety. Driving too fast (taking into account the weight of the trailer, how the load is distributed and recommendations from both the trailer and towing vehicle’s manufacturer), regardless of the posted speed limit, cannot be justified and r 306 will not be relevant.
Australian Emergency Law 
I received this question/comment by email:
In all road/driving questions I say ‘don’t have an accident’ but I think my key point there was ‘don’t exceed the safe rated speed for the trailer (if there is one)’. Where the agency has a policy, whether it’s about towing a trailer or exceeding the speed limit when turning out to the station, that will always be the first point of call when deciding whether ‘it is reasonable that the rule should not apply’ (Road Rules 2014 (NSW) r 306(a)(ii); see also Road Traffic Exemption – Who Determines if it is Reasonable that the Provision Should Not Apply? (May 22, 2016)).
To put that in context; assume the driver is caught by a speed camera doing 120km/h in a 100km/h zone. They are proceeding to an emergency, the red/blue lights are on, the siren is on, the weather is fine, the traffic is light but they have a trailer in tow. An infringement notice is issued and the driver wants to rely on r 306 to say that r 20 (the rule requiring a driver to comply with the speed limit) should not apply in the circumstances.
If the driver asks the SES for support, the SES may well say ‘but our policy say’s don’t drive over the limit’, so is it ‘reasonable’ that the exemption should apply? The SES may out of goodwill write a letter to the police pointing out the emergency and would no doubt, not mention the policy and the police probably won’t know about the SES policy so they may well withdraw the ticket – but assume that doesn’t happen. Assume the SES say they won’t support the application because the driver was driving contrary to their policy. In that case police are unlikely to withdraw the matter so at first instance the policy does determine the outcome.
What if the driver elects to go to court? At that point the prosecutor’s going to know about the policy and that would be the argument – ‘It isn’t reasonable to say that r 20 does not apply when the SES says that it is to apply.’ At the end of the day it would be for the Magistrate to decide taking into account all the circumstances. And a magistrate may be benevolent – it was safe, it was a real emergency, the speed was within the safe rated speed for the trailer etc. But the SES policy would, in my view, be persuasive argument against applying r 306 in those circumstances.
As a professional driving a lot on highways I have seen so many times people driving rented trailers way above the maximum speed. Quite a few times I retrieved some of these vehicles later stopped on the side of the highway with their warning lights blinking. Fortunately I never saw accidents caused by these reckless behaviors but I am sure they do happen.