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From: Sylvia Else on 12 Jul 2010 01:49
<http://www.rta.nsw.gov.au/roadsafety/speedandspeedcameras/speedingresearch.html>

This page illustrates the sleight of hand frequently engaged in the the
RTA and the Government.

"Research has shown that the risk of a crash causing death or injury
increases rapidly, even with small increases above an appropriately set
speed limit."

Yes, apparently, the research does show that. But note the expression
"appropriately set".

Skip down the page a bit, and we see

"Based on this research it can be concluded that
In a 60 km/h speed limit area, the risk of involvement in a
casualty crash doubles with each 5 km/h increase in travelling speed
above 60 km/h."

Whoa there! How did we lose "appropriately set"? The cited research,
which can be found at <http://casr.adelaide.edu.au/speed/>, makes it
clear that the figures relate to a road where the mean free speed is
about 60km/h. The road happens also to have a speed limit of 60km/h, but
the result clearly depends on the mean free speed, not the speed limit.
The paragraph above should say

"Based on this research it can be concluded that
On a road with a mean free speed of 60 km/h, the risk of
involvement in a casualty crash doubles with each 5 km/h increase in
travelling speed above 60 km/h."

We all know of roads where pretty much everyone exceeds the limit
because it's absurdly low. The mean free speed on such roads
significantly exceeds the speed limit.

Sylvia
From: hippo on 17 Jul 2010 10:05
Sylvia Else wrote:
>
>
<http://www.rta.nsw.gov.au/roadsafety/speedandspeedcameras/speedingresearch.html>
>
> This page illustrates the sleight of hand frequently engaged in the the
> RTA and the Government.
>
> "Research has shown that the risk of a crash causing death or injury
> increases rapidly, even with small increases above an appropriately set
> speed limit."
>
> Yes, apparently, the research does show that. But note the expression
> "appropriately set".
>
> Skip down the page a bit, and we see
>
> "Based on this research it can be concluded that
> In a 60 km/h speed limit area, the risk of involvement in a
> casualty crash doubles with each 5 km/h increase in travelling speed
> above 60 km/h."
>
> Whoa there! How did we lose "appropriately set"? The cited research,
> which can be found at <http://casr.adelaide.edu.au/speed/>, makes it
> clear that the figures relate to a road where the mean free speed is
> about 60km/h. The road happens also to have a speed limit of 60km/h, but
> the result clearly depends on the mean free speed, not the speed limit.
> The paragraph above should say
>
> "Based on this research it can be concluded that
> On a road with a mean free speed of 60 km/h, the risk of
> involvement in a casualty crash doubles with each 5 km/h increase in
> travelling speed above 60 km/h."
>
> We all know of roads where pretty much everyone exceeds the limit
> because it's absurdly low. The mean free speed on such roads
> significantly exceeds the speed limit.
>
> Sylvia
>
>

...and nobody ever sems to continue to the bits in various research papers
which pont out that individual drivers travelling significantly *below*
the prevailing speed for that area may also face increased risk of
involvement in accidents.

--
Posted at www.usenet.com.au
From: Sylvia Else on 18 Jul 2010 01:37
On 18/07/2010 12:05 AM, hippo wrote:
> Sylvia Else wrote:
>>
>>
> <http://www.rta.nsw.gov.au/roadsafety/speedandspeedcameras/speedingresearch.html>
>>
>> This page illustrates the sleight of hand frequently engaged in the the
>> RTA and the Government.
>>
>> "Research has shown that the risk of a crash causing death or injury
>> increases rapidly, even with small increases above an appropriately set
>> speed limit."
>>
>> Yes, apparently, the research does show that. But note the expression
>> "appropriately set".
>>
>> Skip down the page a bit, and we see
>>
>> "Based on this research it can be concluded that
>> In a 60 km/h speed limit area, the risk of involvement in a
>> casualty crash doubles with each 5 km/h increase in travelling speed
>> above 60 km/h."
>>
>> Whoa there! How did we lose "appropriately set"? The cited research,
>> which can be found at<http://casr.adelaide.edu.au/speed/>, makes it
>> clear that the figures relate to a road where the mean free speed is
>> about 60km/h. The road happens also to have a speed limit of 60km/h, but
>> the result clearly depends on the mean free speed, not the speed limit.
>> The paragraph above should say
>>
>> "Based on this research it can be concluded that
>> On a road with a mean free speed of 60 km/h, the risk of
>> involvement in a casualty crash doubles with each 5 km/h increase in
>> travelling speed above 60 km/h."
>>
>> We all know of roads where pretty much everyone exceeds the limit
>> because it's absurdly low. The mean free speed on such roads
>> significantly exceeds the speed limit.
>>
>> Sylvia
>>
>>
>
> ..and nobody ever sems to continue to the bits in various research papers
> which pont out that individual drivers travelling significantly *below*
> the prevailing speed for that area may also face increased risk of
> involvement in accidents.
>

The cited research questions whether that effect is real - vehicles amy
be travelling slowly for reasons that put them at higher risk of being
in an accident.

But I'm concerned about the analysis that purports to show a reduction
in fatalities and/or injuries given a reduction in speed. The approach
appears to be to assume that the vehicles involved in a particular
accident would have been in the same relative positions at the start of
the accident sequence, with the lower speeds then resulting in either
reduced impact speeds, or no impact at all. No allowance is made for
drivers making the same basic mistakes, but with the vehicles being
closer when the accident sequence starts. The latter seems entirely
likely with accidents where a vehicle turns across the path of another.

But the RTA isn't really interested in what the research shows. When I
pointed out a fundamental flaw in the analysis that purported to show
that speed cameras reduced fatal accidents[*], the RTA's response was
that similar research overseas had produced similar results (probably by
the same flawed reasoning).

[*] Essentially, they took places where there had been fatal accidents,
typically only one or two, and put speed cameras there. Then they said
"Look, no accidents in the following years". Yet you'd get the same
result if you just identified such places, and did nothing other than
look at the next couple of years - the point being that a small number
of fatalities at a place is just a random event, and the fact that an
accident occurs tells you nothing about what's likely to happen in future.

You could then conclude that doing nothing reduced fatal accidents.

Sylvia.
From: Mr.T on 18 Jul 2010 22:58

"hippo" <am9obmhAc2hvYWwubmV0LmF1(a)REGISTERED_USER_usenet.com.au> wrote in
message news:i1sdbo$mrj$1(a)news.eternal-> ..and nobody ever sems to continue
to the bits in various research papers
> which pont out that individual drivers travelling significantly *below*
> the prevailing speed for that area may also face increased risk of
> involvement in accidents.

Or the fact that fully loaded trucks travelling legally at the speed limit
are FAR more dangerous than a high performance driver in a high performance
car travelling at a speed which will result in an instant loss of license!
(130kph on most multi-lane divided highways)

Hell we can't have facts cloud the issue of revenue after all!

MrT.


From: Mr.T on 18 Jul 2010 23:04

"Sylvia Else" <sylvia(a)not.here.invalid> wrote in message
news:8afi94FevnU1(a)mid.individual.net...
> You could then conclude that doing nothing reduced fatal accidents.

Since the number of fatal accidents has increased in most states in recent
years despite big improvements in speed detection and vehicle safety, you
could certainly argue that their approach is not working.
One thing's for sure, they won't admit the issue is far more complex than
speed alone.

MrT.


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