SA Road Rules in relation to the topic: (sorry for length)
110AAAA—Certain provisions not to apply to drivers of emergency vehicles
(1) Sections 44B, 45A, 82, 83 and 110 do not apply to the driver of an emergency vehicle
if—
(a) in the circumstances—
(i) the driver is taking reasonable care; and
(ii) it is reasonable that the provision should not apply; and
(b) if the vehicle is a motor vehicle that is moving—the vehicle is displaying a
blue or red flashing light or sounding an alarm.
(2) Subsection (1)(b) does not apply to a vehicle used by a police officer if, in the
circumstances, it is reasonable—
(a) not to display the light or sound the alarm; or
(b) for the vehicle not to be fitted or equipped with a blue or red flashing light or
an alarm.
(3) In this section—
emergency vehicle means a vehicle used by—
(a) a police officer; or
(b) a person who is an emergency worker as defined by the regulations for the
purposes of this section.
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44B—Misuse of motor vehicle
(1) For the purposes of this section, a person misuses a motor vehicle if the person—
(a) drives a motor vehicle, in a public place, in a race between vehicles, a vehicle
speed trial, a vehicle pursuit or any competitive trial to test drivers' skills or
vehicles; or
(b) operates a motor vehicle in a public place so as to produce sustained wheel
spin; or
(c) drives a motor vehicle in a public place so as to cause engine or tyre noise, or
both, that is likely to disturb persons residing or working in the vicinity; or
(d) drives a motor vehicle onto an area of park or garden (whether public or
private) or a road related area so as to break up the ground surface or cause
other damage.
(2) However, conduct of a type described in subsection (1) does not constitute misuse of a
motor vehicle if it occurs in a place with the consent of the owner or occupier of the
place or the person who has the care, control and management of the place.
(3) A person who misuses a motor vehicle is guilty of an offence.
(4) A person who promotes or organises an event involving the misuse of a motor vehicle,
knowing that it will involve the misuse of a motor vehicle, is guilty of an offence.
(5) Where a court convicts a person of an offence against this section, the court must, if
satisfied that the offending caused damage to, or the destruction of, any property or
damage to an area of park or garden or a road related area, order the convicted person
to pay to the owner of the property, or the owner, occupier or person who has the care,
control and management of the area, such compensation as the court thinks fit.
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45A—Excessive speed
(1) A person who drives a vehicle at a speed exceeding, by 45 kilometres an hour or
more, a speed limit that applies under this Act or the Motor Vehicles Act 1959 is guilty
of an offence.
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82—Speed limit while passing school bus
(1) A person must not drive a vehicle at a greater speed than 25 kilometres per hour while
passing a school bus that has stopped on a road apparently for the purpose of
permitting children to board or alight.
(2) In this section—
school bus means a bus that displays the warning signs and devices required by the
vehicle standards for buses used mainly for carrying children.
83—Speed while passing emergency vehicle with flashing lights
(1) A person must, while passing an emergency vehicle that has stopped on a road and is
displaying a flashing blue or red light (whether or not it is also displaying other
lights)—
(a) drive at a speed no greater than 40 kilometres per hour; or
(b) if a lesser speed is required in the circumstances to avoid endangering any
person—drive at that lesser speed.
(2) Subsection (1) does not apply if the person is driving on a road that is divided by a
median strip and the emergency vehicle is on the other side of the road beyond the
median strip.
(3) In this section—
emergency vehicle means a vehicle used by—
(a) a police officer; or
(b) a person who is an emergency worker as defined by the regulations for the
purposes of this section.
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110—Driving on sealed surface
A person driving a vehicle on a road which has portion of its surface sealed with
bitumen, cement or other sealing substance must, whenever it is reasonably
practicable to do so, keep the whole of the vehicle on the sealed portion of the surface.
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Note that you can still be charged with driving without due care & driving in a manner dangerous. So regardless you have to justify your actions and speed etc.
I think SAAS send out a please explain form if you get done at over 40km/h and it is reviewed by a judge/magistrate who decideds what action (if req) will be taken.
Also I think anything over 20km/h services get sent a please explain (or need to have appropriate data to justify the response, so case number and response category etc I guess)