Speeding Rules

by Petrol Mum
Audi RS 6 Avant driving

Have you ever noticed how sometimes the display on your vehicle’s speedometer is different from the speed shown on the navigation app on your phone? You’re not alone. And it’s all to do with Australian Design Rules (ADRs).

The ADRs are set by the Department of Infrastructure, Transport, Regional Development, Communications, and the Arts and are the national standards for road safety and specify how a car should be designed and made fit for purpose when it’s sold in Australia.

According to the ADRs, car manufacturers are prohibited from under-reporting a vehicle’s speed. As a result, vehicle manufacturers often calibrate the speedometers at the factory so that it reads above the actual real speed of the car.

Road safety expert, Emeritus Professor Michael Regan from the University of New South Wales, says most manufacturers do this to avoid any chance whatsoever the car might be travelling at a speed that is higher than the reading on the dashboard.

 “ADRs require a speedo tolerance of zero per cent under to 10 per cent above the actual speed, so manufacturers typically set it at about five per cent over,” Prof. Regan says.

 “This means the speedo is likely to read 100 kilometres per hour when, in actual fact, your real speed is 95 kilometres per hour.”

The displayed speed that you’re travelling on the road is determined by the vehicle’s tyres. Speedometers are calibrated to read based on the rate of revolution of the car’s power train. This, in turn, depends on the tyres and it’s usually on a set of new tyres of a certain circumference. But over time, as the tyres experience normal wear and tear, they get smaller in circumference. This changes the accuracy of the reading of the speedometer – again showing a higher speed than the actual speed.

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Commonly these days many drivers use mobile navigation apps which also measure and display the speed being travelled within the interface. But unlike the speedometer, these apps take advantage of global positioning satellite (GPS) technology to calculate speed by determining the time taken to travel a given distance.

As a result, the GPS speed is often hailed as being more accurate than the car’s speedo, says Prof. Regan.

“If you’re driving on a flat, straight road, the GPS is likely to be more accurate than what’s displayed on your speedo.

 “However, if you’re going up or down a steep hill, the actual speed (for example, as measured by Police mobile radar) will usually be greater than the GPS value but proportional to the steepness of the road you’re travelling on.

 “It is the change in elevation, relative to the GPS satellites circling above, that results in the error. Horizontal bends do not affect it.

“In theory a clever GPS device could account for the road steepness and adjust the displayed speed so it is more accurate. However, this is a relatively rare situation and there is no strong justification for navigation devices to make this adjustment. Drivers should just bear this factor in mind when driving on steep roads.

 “To be absolutely sure how fast you’re driving, you need to know how much the car’s speedo is out by.”

Prof. Regan says the important next step in car safety technology is implementing intelligent speed assistance (ISA) systems, which have been shown in numerous studies to be highly effective in reducing speeding, and speed-related crashes.

ISA relies on GPS and/or built-in cameras on the car to detect and read traffic signs and lets the driver know in real-time what the speed limit is. ISA systems come in two basic forms. Advisory ISA systems can issue a warning to the driver if they exceed the speed limit. Such systems have been in existence for more than two decades.

 “More advanced limiting ISA systems can physically prevent the vehicle from exceeding the posted speed limit; like a conventional speed limiter, but a more intelligent one,” he says.

 “Like adaptive cruise control, the driver is always in control and can easily override the ISA system.

 “This is just another example of how systems can be implemented to improve road safety because the reality is that sometimes drivers can become distracted and miss changes in speed signs, or simply not realise that their speed has creeped up.”

 Through its star safety rating system, the Australasian New Car Assessment Program (ANCAP) has encouraged fitment of these speed assistance systems for more than a decade, and assesses vehicles based on the presence of ISA and its performance. But ANCAP is a voluntary program and there is no equivalent requirement in the mandatory ADRs.

Artificial intelligence (AI) or autonomous driving technology is becoming a mainstay in Australian automotive. This has been encouraged in part by the Australasian New Car Assessment Program including “active safety” technology as part of its new safety rating criteria as of January 2023.

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A recent survey undertaken by Savvy, one of Australia’s largest online financial brokers, focusing on personal and commercial financial products, found that 47% of Australians have some level of concern about AI or autonomous driving features. Our level of concern is dependent on our age with 26% of 18–24-year-olds trusting autonomous driving compared with just 5% of over 55s.

Other active safety measures Australians consider important in a car purchase are blind spot monitoring (50%), emergency braking systems (32%), adaptive cruise control (28%), and lane change assist (18%). Women were more likely to choose safety features over men, such as 56% of women choosing 360° cameras as important compared with 48% of men and 37% of women versus 27% of men saw emergency braking as important.

Each year, speeding contributes to about 41 per cent of road fatalities and 24 per cent of serious injuries in New South Wales alone. Prof. Regan says that just because our speedometers are calibrated to overstate our speed, this does not give the green light for drivers to engage in excessive speeding.

Photographs by Driven Women Magazine.

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