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Speedometer
Accuracy
If
a speedometer is not accurate, it could
display a lower speed than the vehicle
is actually travelling at, thus causing
drivers to believe they are not
speeding when in fact they are. This
effect can occur if a speedometer
under-reads true speed.
- A
speedo over-reads if it displays
100kmh when the vehicle's actual
speed is 90kmh.
- A
speedo under-reads if it displays
100kmh when the vehicle's actual
speed is 110kmh.
The
actual speed can be easily determined
these days using GPS (Global
Positioning System). I use a meridian
GPS unit which can display speed to the
first decimal place. Motorists should
have their speedos calibrated to ensure
it is as accurate as is reasonably
possible. Up until July 2006 the
Australian Design Rules required new
cars to have speedos that are accurate
to within 10% of actual speed. The
current Rules disallow under-reading,
and permit over-reading by up to 4kmh +
10%.
Speedometer
Errors
Several factors can affect the
accuracy of speedometers:
Worn
tyres: As the rubber on the tyre
wears, the tyre diameter becomes
smaller. This will make the wheel
travel a shorter distance per
revolution. Your speedometre might
think one revolution is 170cm, but due
to tyre wear it is in fact 167cm. So a
car running at the same RPM will
actually travel less distance. Instead
of covering 100km in one hour, it goes
only 99km. As the rubber wears, the
vehicle's actual speed drops relative
to the displayed speed. Because speedos
should always be calibrated when tyres
are new, not when they are worn,
driving on worn tyres will mean your
speedo over-reads. Actual speeds will
always decrease relative to a fixed
displayed speed as the tyres wear.
Having worn tyres can not cause you to
speed inadvertently.
Tyre
Pressure: If you decrease the tyre
pressure, the diameter of your wheel
decreases and the wheel will travel a
shorter distance per revolution. This
will decrease the actual speed of your
vehicle in comparison with the
displayed speed. If you drive with low
pressure in your tyres you reduce the
risk of unknowingly driving over the
speed limit. Because speedos should
always be calibrated when tyres are
fully inflated, driving on low pressure
tyres cannot cause your speedo to
under-read. However, heat build-up or
over inflation could possibly cause the
tyres to balloon slightly which can
increase their diameter and could
theoretically cause under-readings if
there were no other factors offsetting
this error.
Rim
size: If you change the diameter of
your wheels you will affect the
accuracy of the speedo. Changing from
16 inch wheels to 17inch wheels does
not necessarily change the total
diameter of the wheel. It depends a lot
on the type of tyre that is used.
Changing to a wider diameter rim will
usually result in a larger diameter
wheel. A larger wheel causes your car
to travel further with each revolution.
If the speedo is not recalibrated it
may under-read, which will mean your
actual speed might be greater than that
displayed on your speedo. If you are
increasing the rim size of your tyres,
you should recalibrate your speedo to
make sure you do not inadvertently
exceed the speed limit.
Differential
ratios: Changing the gear sizes in
your vehicle's differential or gear box
can affect the accuracy of the
speedometer, resulting in either
over-reading or under-reading depending
on what the change was.
Vehicle
load: When you load your car the
tyres carry more weight, which can
cause them to depress slightly and have
a smaller diameter. This can cause an
over-reading. It can never cause
under-reading. It can not cause you to
exceed the speed limit unknowingly.
Just as you calibrate your bathroom
scales when there is no weight onboard,
so too are car speedos calibrated when
there is no extra load on the
tyres.
Speedo
Displays: Many modern speedos
display in increments of 5 kmh and do
not easily display speeds down to 1kmh
accuracy. The needle mechanism has its
own accuracy limitations. Some old
vehicles will have faulty speedos or
they have fallen out of calibration, or
the needle may wag up and down slightly
making it difficult to determine
exactly what speed is being
displayed.
Speedo
Needles: The size and shape of
needles can make it difficult to tell
exactly what speed is displayed. Given
the variables mentioned above, the
observable displayed speed is a
reasonably accurate, and usually
conservative, estimate of actual
speed.
These potential errors have been
widely
known for decades.
Australian
Design Rules (ADR)
When
vehicle manufacturers install a speedo
at the factory, the speedo has been
calibrated using data that assumes the
vehicle is fitted with new standard
tyres inflated to full pressure, on
standard rims, and usually with the
tyre circumference measured before the
wheel is put on a vehicle or when the
vehicle is on a hoist (no load on
tyre). When they test the car for
compliance with the ADR, the speedo
will invariably produce an over-read
result.
The
current Australian
Design Rules
require speedos to be calibrated when
the vehicle is unladen, fitted with
normal tyres inflated to full pressure
with an allowance for tyre
heating:
- "Unladen
vehicle" means the vehicle in
running order, complete with fuel,
coolant, lubricant, tools and a
spare wheel (if provided as standard
equipment by the vehicle
manufacturer), carrying a driver
weighing 75 kg, but no driver's
mate, optional accessories or
load.
- "Tyres
normally fitted" means the type or
types of tyre provided by the
manufacturer on the vehicle type in
question; snow tyres shall not be
regarded as tyres normally
fitted;
- "Normal
running pressure" means the cold
inflation pressure specified by the
vehicle manufacturer increased by
0.2 bar.
-
The
current ADR prohibits any
under-reading:
- "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."
This
formula means that the vehicle's actual
(true) speed must not be greater than
the displayed speed. (Displayed speed
minus true speed must be greater than
or equal to 0, and less than or equal
to 4kmh plus 10% of true speed). This
means that if your vehicle's actual
speed is 100kmh, the displayed speed is
permitted to be anywhere between 100kmh
and 114kmh.
Prior
to July 2006 the ADR allowed ±10%.
This means that cars sold new prior to
1 July 2006 could comply with the ADR
even if the speedo under-read by 10%.
Despite this being theoretically
possible, due to the testing procedures
and the reasons stated below it is
unlikely to occur in practice.
The reason
the ADR are relevent to the debate is that some people argue that if
the ADR allows cars to have speedos that under-read by up to 10%, then
surely our road laws must also allow 10% tolerance. Therefore, the
argument goes, we should not be fined if we travel at 110kmh in a
100kmh zone because we are travelling within the tolerances allowed by
the ADR. Such a situation would be quiet generous to motorists and
would make it impossible for anyone to allege that they were mislead by
their inaccurate speedo.
One
problem with this argument is that it
ignores reality. It assumes that
speedos are under-reading by 10% when
the truth is the vast majority of
speedos over-read by about 3%. So in
effect, it is allowing the majority of
motorists the opportunity to drive at
10% above the speed limit. If the speed
limits are there for a reason, then
they would all need to be reduced by
10% to counter the effect of motorists
increasing their speed above it.
If
a motorist has a speedo that
under-reads by any amount, then that person could try to argue that they have a defence of "honest
and reasonable belief" in a state of
facts which if true would make their
conduct innocent. (See Proudman
v. Dayman). Even if it were available, a Proudman v. Dayman defence is not
dependant on the existence of the
Australian Design Rule specification. A
court is concerned with what your
speedo actually displays, not what the
ADR says it could display. If your
speedo under-reads and there is no ADR
speedo specification in existence, your
defence would be exactly the same. The amount of
tolerance specified in the ADR is
irrelevant to any defence at law. Any
driver who relies on the old ADR for
their belief that their speedo was
accurate would probably fail because
the old ADR does not require a speedo
to be accurate. It allowed it to be out
by up to 10% so you should know it is out by 10%. And if you want to argue
that the ADR is a "law" which applies
to the State of Victoria, then you also
need to argue that ignorance of the law
is no excuse, and therefore you are
deemed to have known that your speedo
was up to 10% under-reading and you had
no basis for assuming it was correctly
displaying your speed at the time of
the alleged offence.
If having an
incorrect speedo were a defence to speeding then all you need to do is
ensure your speedo is wrong and you will never have to pay a fine. If
the inaccuracy of your speedo is merely a theoretical possibility, then
that just turns a weak argument into a hopeless one because you are not
addressing what in fact happened to you on the date of the offence.
For
most of the 20th century there was no
requirement that cars be fitted with
speedos, seat belts and many other
items we all take for granted these
days.
Relevance
of speedo errors in
court
It
is sometimes suggested that the
inaccuracy of speedometers could be
used in court as a defence to a
speeding charge. The basis is that the
driver will allege that he or she was
mislead by the incorrect speedo.
Clearly an over-reading can not be
relevant in any defence, because then
the driver would be travelling slower
than the displayed speed. You must have
an under-reading if you want to allege
that you exceeded the speed limit
because you were mislead by your
speedo.
Traffic offences fall into two categories. There are strict liability offences and absolute liability offences.
A strict liability offence
is one where the prosecution does not need to prove that you knew that
what you were doing was unlawful. e.g. driving whilst suspended is a
strict liability offence. It is still a defence if the state of the
defendant's knowledge is raised as an issue in the proceeding and then
the prosecution carry the burden of satisfying the court that the
defendant did not have an honest and reasonable belief. In such cases
there is no obligation on the defendant to satisfy the court that
he/she had an honest and reasonable belief in a state of facts which if
true would have meant that no offence had been committed once the issue
of mens rea has been raised.
An absolute liabilty offence
is one where the only thing that matters is the actus reas and mens rea
is always irrelevant. That means the actions of the defendant are
relevant and his or her state of mind is never relevant. In victoria
such offences include disobeying traffic signs, exceeding the speed
limit and drink driving.
Most motor
traffic offences are absolute liability offences where the driver's
state of mind is never relevant. In Victoria, the Supreme Court has
said in the case of Kearon v. Grant that the offence of exceeding the
speed limit is an absolute liability offence. That means, not
only does the prosecution not need to prove that the driver had
knowledge that he or she was committing an offence, but the defendant
can not even raise the issue of their state of mind in their defence.
It is no defence for a driver to say "I did not realise I was speeding".
Generally the harsher the penalty is (e.g. punishable by imprisonment),
the more likely the traffic offence will be a strict liabilty offence,
although drink driving appears to be an exception to this rule.
If your car's
speedo does actually under-read, then despite it being a strict
liabilty offence some people will try to argue this as a defence
in court. The possibility for this is is greater since the new ADR came
out. The new rules require new cars never to under-read, so if yours
does then it fails to comply with the new ADR. This will support a
defence of honest and reasonable belief.
To win using this defence
it is necessary for the driver to show
that they had an honest belief that
they were driving lawfully at the time,
and that it was reasonable for them to
hold that belief. It is not an easy
defence to run.
If
you modify your vehicle by changing
wheel sizes or gear ratios, then it is
reasonable to expect that the speedo
will become inaccurate and may
under-read true speed. Any court will
say that a driver who chooses to drive
without checking whether the
modifications have affected their
speedo, or without having the speedo
re-calibrated is reckless as to the
accuracy of their speedo. In those
circumstances the driver should not
expect the court to accept that it was
reasonable for the driver to form a
belief that he or she was driving
within the speed limit based on the
display of an inaccurate
speedo.
The
usual wear and tear factors outlined
above all work to increase the
displayed speed (making it display a
speed greater than actual speed), and
therefore can not form the basis of an
honest and reasonable belief defence.
There is no defence available unless
the speedo has erroneously displayed a
speed lower than actual speed. i.e. the
speedo displays 100kmh when your actual
speed was 115kmh. Tyre wear, carrying
heavy loads and low tyre pressure all
result in over-readings and thus defeat
the argument.
In
order to obtain any significant
under-reading in your speedometer you
will need to modify your vehicle.
Fitting tyres with thicker tread or
over inflating will barely account for
the 1% - 2% deduction already built
into speedos at factory. If you are
driving a modified vehicle no
magistrate is going to accept that it
was reasonable to assume the speedo
would remain accurate.
If
you have purchased a second-hand car,
it may be possible that you did not
know that any modifications had been
made. It is still a hard task to
convince a magistrate that it was
reasonable for you to trust that the
speedo was accurate on your second hand
car, particularly when they are not
calibrated as part of the RWC testing.
If you get your speedo checked and find
it is under-reading, then you no longer
have any basis for trusting that it is
accurate.
If
you want to allege that it is too
difficult to read your speedo down to 1
kmh (because of the graduations on the
display, or the size of the needle),
then the court will expect you to err
on the side of caution when driving. In
any case, all that is required is for a
speedo to indicate if you are lover or
under 60kmh or 80kmh, for example.
There is no requirement, either legal
or practical, for a speedo to
accurately display a speed of 87kmh,
because we do not have any 87kmh zones
in Australia. The speedo needs to
indicate if you are over the limit. So
claiming your needle or display makes
it hard to determine if your speed was
102kmh or 104kmh is unlikely to get you
anywhere. A court will expect you to
keep the middle of the needle below the
100kmh graduation mark when in 100kmh
zones, and that a person who drives
over the limit because they could not
clearly read the exact speed must have
been reckless as to whether or not they
were committing an offence. This is not
a defence. The court expects drivers to
make sure they are driving within the
law.
If you want to argue that the old ADR allowed
How
to defend a speeding charge based on an
incorrect speedo
Prior
to July 2006 the Australian Design
Rules required speedos on new cars to
be accurate to within 10%. It was lawful
for a new car to have a speedo which
under-read by 10%. Speedos are not
covered by Victoria's roadworthy laws
and are not checked as part of
roadworthy tests. If you are booked for
doing 110kmh in a 100kmh zone, and you
then get your speedo checked to find
that it is under-reading, then you
might think you have a good defence
based on your mistaken belief that you
were not speeding. Traffic offences
generally fall into two classes: Strict
liability and absolute liability (read
He Kaw Teh).
It
is a defence to strict liability
offences for the defendant to show that
he or she had an honest and reasonable
belief in a state of facts which if
true would mean that no offence would
have been committed (e.g. Proudman v.
Dayman). If this is shown, the
prosecution then have to prove beyond
reasonable doubt that the defendant did
not hold an honest and reasonable
belief.
Then
we have absolute liabilty offences, and
the Victorian Court of Appeal
decided in 1990 (Kearon v. Grant) that
speeding offences are absolute
liabilty offences for which a defence
of honest and reasonable mistake does
not exist.
If
you want to try to overrule Kearon v.
Grant (by taking your case to the Court
of Appeal or the High Court) you will
need to rely on the Proudman v. Dayman
defence. You will need the following: a
relatively new car (factory
configuration, not worn out), an
engineer's report that shows how much
the speedo under-reads, the opinion of
an expert to say that at the time when
the vehicle was being driven at the
speed detected by the police, the
vehicle's speedo displayed a speed that
was within the speed limit, and
evidence from the driver to say that he
had an honest and reasonable belief
that at the time of driving he believed
his speedo was accurate, that it
displayed a speed within the speed
limit at the time of the offence and
that he relied on his speedo to
determine what speed he was driving
at.
A court is
unlikely to accept this defence if your actual speed was so high that
even an inaccurate speedo would have displayed an illegal speed, or if
you did not have good reason to trust your speedo was accurate, or if
you can not prove your speedo is in fact under-reading. You will need
to run this case through the Magistrates Court, then the Supreme Court
and then to the Court of Appeal (and possibily even to the High Court)
if you want to over-rule the decision in Kearon v. Grant.
Before
you embark on court proceedings in a
case like this, you might wish to try
writing to the Penalty Review Board at
the Traffic Camera Office (Level 1, 277
William Street, Melbourne)
enclosing a copy of the engineers
report and calibration test results,
and ask them kindly to withdraw the
notice. It has been known to happen.
Police
allowances
Victoria
Police guidelines require a deduction of 2kmh or 3kmh from the speed
reading displayed by prescribed speed measuring devices, depending
which device was used. This is to avoid contested cases where the only
argument in court is in respect of the ability of the police device
accurately to measure speed down to the last 1kmh. The deduction they
allow varies for each device depending on the calibration tolerance
required by the legislation for that device. The legislation does not
require any deduction to be made, it just requires the device to be
accurate to a certain degree. The 2 or 3kmh deduction allowed by the
police is to take into account potential inaccuracies in the police
speed measuring equipment. i.e. the laser or radar device might be 1%
over-reading. The deduction allowed for by the police is not
intended to provide any allowance for potential inaccuracies in
motorists' speedos, although they will allege that it has that effect.
An
unfair system
The above is an analysis of the law
as it is at the moment. Debate may rage
about whether police guidelines, or the
law, should give greater allowances to
motorists. There is nothing wrong with
having speed limits on Victoria's
roads, and nothing wrong with enforcing
those limits. A line needs to drawn
somewhere. The real issue is with
penalties. Speeding fines can be easily
incurred from a moments lack of
concentration on speed signs, or on the
speedo. The harsh consequences of
licence loss from excess demerit points
should not be inflicted on people who
are detected driving 4kmh over the
speed limit. A much fairer
solution would be to issue small fines
(up to $60) with no demerit points for
speeds up to 8kmh over the speed limit.
(This is similar to what they have in W.A.) 1 demerit point is fair for 9kmh to
15kmh over the limit, 3 points for
anything over 15kmh above the limit. In
Victoria drivers more than 25kmh over
the limit get mandatory licence loss, so why do they have to suffer up to 8
demerit points as well? Demerit points
should only be recorded against people
who are avoiding
immediate licence loss. At present in
Victoria, drivers travelling 35kmh over
the limit get 6 months licence loss
plus 6 demerit points, which means they
risk suffering suspension twice for the
same offence. This is clearly wrong.
Drink drivers get demerit
points only if they keep their licence.
If they lose their licence, they get no
points because they are already
suffering a licence loss punishment and
should not have to do it twice.
Mandatory licence loss laws in Victoria
leave the courts with no discretion to
apply a more reasonable and fairer
penalty to suit the circumstances of an
offence or of the offender. Perhaps the
courts should have more discretion in
licence suspension and cancellation
cases so that the usual sentencing
principles can be applied in those
cases.
Speedo
Accuracy, faulty speedo, speedo
inaccuracy, inaccuracies, speedo
errors, speedo margins or error, wrong
speedo reading, erroneous speedo,
defective speedo, mph speedo, broken
speedo, speedo misreading, speedo false
reading. speedometre
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Getting
Legal Advice
Fines
Demerit
Points
Speeding
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