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From: Sylvia Else on 11 Jul 2010 08:15
http://www.rta.nsw.gov.au/roadsafety/downloads/nsw_sza.pdf

"2.3.6.3 85th percentile speed of vehicles
Speed surveys are used to determine overall traffic
speed and volume on a road. This speed is usually
determined by a survey of vehicles travelling under
free-flow conditions. One of the measures used is the
85th percentile speed, which is the speed at or below
which 85% of drivers travel.
This measure is useful for designing, implementing and
evaluating speed management initiatives to address
a speeding problem on a length of road. It does not
indicate the safe speed limit."

Sylvia.
From: Sylvia Else on 11 Jul 2010 09:12
On 11/07/2010 10:36 PM, Toby wrote:
> On Sun, 11 Jul 2010 22:15:37 +1000, Sylvia Else wrote:
>
>> http://www.rta.nsw.gov.au/roadsafety/downloads/nsw_sza.pdf
>>
>> "2.3.6.3 85th percentile speed of vehicles
>> Speed surveys are used to determine overall traffic
>> speed and volume on a road. This speed is usually
>> determined by a survey of vehicles travelling under
>> free-flow conditions. One of the measures used is the
>> 85th percentile speed, which is the speed at or below
>> which 85% of drivers travel.
>> This measure is useful for designing, implementing and
>> evaluating speed management initiatives to address
>> a speeding problem on a length of road. It does not
>> indicate the safe speed limit."
>>
>> Sylvia.
>
> Yeah - right.
> Drivers are NOT permitted to decide what 'speed' is safe - is that what's
> being said?

Pretty much. I suppose the RTA might argue that there can be particular
road situations where drivers' perceptions are flawed, leading them to
drive faster than is safe. Indeed that might be true, but I think a
"Deceptive Road Conditions Ahead" sign would be more useful than a low
limit, which will just look like a typical Nanny State absurdly low
speed limit and be largely ignored unless a speed camera is installed.

The paragraph following the one I quoted indicates that one approach
that can be used when it is observed the 85th percentile is above the
speed limit is to reduce the latter. Of course, the result will be an
even greater mismatch between speed limit and 85th percentile speed.
This just shows how poor is the thinking behind the document.

Sylvia.
From: Toby on 11 Jul 2010 09:38
On Sun, 11 Jul 2010 23:12:18 +1000, Sylvia Else wrote:

> On 11/07/2010 10:36 PM, Toby wrote:
>> On Sun, 11 Jul 2010 22:15:37 +1000, Sylvia Else wrote:
>>
>>> http://www.rta.nsw.gov.au/roadsafety/downloads/nsw_sza.pdf
>>>
>>> "2.3.6.3 85th percentile speed of vehicles
>>> Speed surveys are used to determine overall traffic
>>> speed and volume on a road. This speed is usually
>>> determined by a survey of vehicles travelling under
>>> free-flow conditions. One of the measures used is the
>>> 85th percentile speed, which is the speed at or below
>>> which 85% of drivers travel.
>>> This measure is useful for designing, implementing and
>>> evaluating speed management initiatives to address
>>> a speeding problem on a length of road. It does not
>>> indicate the safe speed limit."
>>>
>>> Sylvia.
>>
>> Yeah - right.
>> Drivers are NOT permitted to decide what 'speed' is safe - is that what's
>> being said?
>
> Pretty much. I suppose the RTA might argue that there can be particular
> road situations where drivers' perceptions are flawed, leading them to
> drive faster than is safe. Indeed that might be true, but I think a
> "Deceptive Road Conditions Ahead" sign would be more useful than a low
> limit, which will just look like a typical Nanny State absurdly low
> speed limit and be largely ignored unless a speed camera is installed.
>
> The paragraph following the one I quoted indicates that one approach
> that can be used when it is observed the 85th percentile is above the
> speed limit is to reduce the latter. Of course, the result will be an
> even greater mismatch between speed limit and 85th percentile speed.
> This just shows how poor is the thinking behind the document.
>
> Sylvia.

But then we get into strife believing that the 85th is actually based
merely on a perception of risk.
But it isn't as soon as the propaganda machine has it's way with drivers
performance.
It's probably the case that the 85th percentile is influenced by the
anti-speed propaganda - even the top 15% of people may be altering their
behaviour so suite the accepted stance of society. That Speed kills.
Worth thinking about - because as soon as this begins to effect drivers in
any numbers, we'll see GovCo having a major win which it most assuredly
does NOT deserve - especially as GovCo has achieved that 'win' entirely at
the expense of the community. Worse, we let 'em do it.
--
Toby.
Caveat Lector
From: Jason James on 11 Jul 2010 17:02

"Sylvia Else" <sylvia(a)not.here.invalid> wrote in message
news:89tu9kF8gmU1(a)mid.individual.net...
> On 11/07/2010 10:36 PM, Toby wrote:
>> On Sun, 11 Jul 2010 22:15:37 +1000, Sylvia Else wrote:
>>
>>> http://www.rta.nsw.gov.au/roadsafety/downloads/nsw_sza.pdf
>>>
>>> "2.3.6.3 85th percentile speed of vehicles
>>> Speed surveys are used to determine overall traffic
>>> speed and volume on a road. This speed is usually
>>> determined by a survey of vehicles travelling under
>>> free-flow conditions. One of the measures used is the
>>> 85th percentile speed, which is the speed at or below
>>> which 85% of drivers travel.
>>> This measure is useful for designing, implementing and
>>> evaluating speed management initiatives to address
>>> a speeding problem on a length of road. It does not
>>> indicate the safe speed limit."
>>>
>>> Sylvia.
>>
>> Yeah - right.
>> Drivers are NOT permitted to decide what 'speed' is safe - is that what's
>> being said?
>
> Pretty much. I suppose the RTA might argue that there can be particular
> road situations where drivers' perceptions are flawed, leading them to
> drive faster than is safe. Indeed that might be true, but I think a
> "Deceptive Road Conditions Ahead" sign would be more useful than a low
> limit, which will just look like a typical Nanny State absurdly low speed
> limit and be largely ignored unless a speed camera is installed.
>
> The paragraph following the one I quoted indicates that one approach that
> can be used when it is observed the 85th percentile is above the speed
> limit is to reduce the latter. Of course, the result will be an even
> greater mismatch between speed limit and 85th percentile speed. This just
> shows how poor is the thinking behind the document.
>
> Sylvia.

On a related note, who decides what speed advisory speed is posted on the
approach to corners? I have noticed that virtualy everyone ignores these
signs. If they did, you'd have a dramatic slowing of highway traffic. It
seems they are posted for the benifit of low-loaders carting half a house
:-)

Jason


From: Feral on 11 Jul 2010 17:09
Jason James wrote:

> On a related note, who decides what speed advisory speed is posted on the
> approach to corners? I have noticed that virtualy everyone ignores these
> signs. If they did, you'd have a dramatic slowing of highway traffic. It
> seems they are posted for the benifit of low-loaders carting half a house
> :-)

Or Bean and Fawlty types of cars. ;-)

--
Take Care. ~~
Feral Al ( @..@)
(\- :-P -/)
((.>__oo__<.))
^^^ % ^^^
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