Check Your Speed Signs

One of the most useless official signs I have seen on our highways are the “Check Your Speed” signs comprising 6 signs numbered 1 to 6 at 1 Km intervals.
What do they expect you to do? Illegally pick up your smart phone so as to utilise its stopwatch function? That is if you are even able to maintain a constant speed whilst dealing with other traffic.
Why don’t they just provide the solar powered speed detectors with the clearly visible digital readouts instead?
They are already installed in some built-up areas and temporarily placed during some roadworks.
They just take a momentary glance to check your speed instead of distracting drivers’ concentration in watching their speedo, the signs and everything else.
Perhaps they do not want motorists becoming aware that their speedos are factory set to read higher than the true speed their vehicles are travelling at.


I assume those signs are an older method of allowing you to check If your Speedo is out/by how much, but they do require you to do some math on the fly. Regardless of the speed you pass those signs at, if you observe your kms traveled as you pass the first and last signs, you can calculate how far your Speedo is out.

E.g. If after 5km your car says it’s traveled 5500m, then your car Speedo is likely about 10% out (this may be less reliable on cars with digital readouts; not sure, depends how they mechanically record speed/distance traveled under the bonnet)



There is an article on the ABC News website about speedos.

There is also a link to a RACQ article.
So at 100 Km, the speedo can be reading as much as 14 Km high.
There is no longer any requirement for odometer accuracy.


No, there is, see section 18.5 on page 7:

Speedos are required to overestimate the vehicles speed.


My bike has a pin on the dial that stops the needle just after the last number - from about that point on it reads under actual speed … :wink:


Vehicle Standard (Australian Design Rule 18/03-Instrumentation) 2006 states under section 5.3 on page 13
5.3. The speed indicated shall not be less than the true speed of the vehicle. At the
test speeds specified in paragraph 5.2.5. above, there shall be the following
relationship between the speed displayed (V1 ) and the true speed (V2).
0 ≤(V1 - V2) ≤0.1 V2 + 4 km/h
There is no mention of odometers.
It appears that the RACQ is correct as one would certainly expect them to be.


I just use the GPS on my mobile. And yes I only do so when there are two of us in the car. One driving and one with the mobile in hand. That way you can choose on which section of the road to use and wait for suitable traffic conditions. All legal.

I have used an app on iphone - Speedometer v1.81 that works a treat. The longer the time the more accurate the result. It can measure instantaneous speed, average speed and distance to GPS accuracy. Usually try to hold a speed for at least 2 to 3km. The distance traveled is a great check against the cars trip meter. There are other apps that do essentially the same for any GPS phone. I just find the Apple app store easy to search, and low risk compared to the Android alternatives. There is also an android phone in our house if you are wondering why the comparison.

I have also had an opportunity to check the apparent accuracy of the app against the speed displayed in a Shinkansen Hikari service. Not as fast as a rare European hyper sports car, but much more affordable, safe, legal and no need to pull over and refuel with 98 every 50km or so. The app passed my test.


What a classic reply.

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