Speed research

This came up on the MCC delegates list, from Guy:

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http://www.atsb.gov.au/road/rpts/cr204/index.cfm


This is the oft-quoted research that report that is used to justify
speed limit reductions.

There are some who have raised issues with the methodology and "controls"
used in the case control study. e.g. the control used for a vehicle
that collided with a U-turning vehicle was a vehicle travelling at "free
speed" at the same time of day and day of week and this concludes that
the cause of death was excess speed of the "free speed" vehicle, rather
than presence or absence of a U-turning vehicle. I have some difficulty
with this too.

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Also see this rtf file (1mb or so)
http://tinyurl.com/2h89c

Which is a review of the research, with somewhat different ideas as to
what it means.

CONCLUSIONS
Re-analysis of the original data shows that:
Driver selection of travel speed is based on many factors, with
the prevailing speed limit and speed enforcement being only two of these
factors;
In a 60 km/h limit zone, average free speeds on dry days during
daylight hours exhibit significant variability;
A more consistent approach to the data is to use speed
differentials from the mean speed, and that approach produces a U shaped
risk curve.

VicRoads speed monitoring data reveals that on those sections of roads
where speed enforcement is most likely to occur, mean speeds are likely
to be high, and in the range of 65 – 67 km/h. Given this fact and the
risk curve above, the use of a 10 km/h enforcement tolerance, and the
setting of 15 km/h as the next level of enforcement represent a fair
approach to speed enforcement.

However the author agrees with the finding of the original report that
the penalties at 15 km/h or higher above the speed limit should be
increased based on the very rapid increase in crash risk.

=======

 

I also love the fact that for speeds above 88 km/h the risk becomes
infinite - that is your risk of involvement in a casualty crash is no
longer a risk but a certainty! Talk about rubbish...

Agree with the control vehicle selection. Four vehicles per case
vehicle seems insufficient to be a true gauge of traffic speed to me.

Also, the fact that one of the selection criteria was that ther had to
be a casualty influences the results. Crashes at higher speeds involve
greater crash energies and obviously a resulting higher likelihood of
injury. This means that incidents become self selective - the higher
speed makes hospital transport more likely and thus the crash more
likely to be included in the study.

It tells us nothing about the relationship of travel speed to crash
likelihood only that if you crash at higher speeds you are more likely
to be transported to hospital - well gee, what a stunning insight!

It does not automatically relate that the speed of the vehicle was the
cause of the crash. Surely to evaluate speed as a *cause* then all
crashes would need to be evaluated. I would be very interested to see
the results if they included this.

I have read other reports that rip Kloeden et als research apart, and
if this report was being presented for publishing in any reputable
scientific journal, rather than to a govrenment body, I suspect the
authors would be asked to review their findings.

Another example of a bunch of government funded researchers turning
out results that mysteriously support the stance, policy and aims (and
propaganda) of the government body funding them. Keeps those research
funds flowing I guess. After all, recently Carl Scully demonstrated
just how (un)willing he is to consider differing research on speed
when a UK researcher presented strong evidence that speed cameras
don't work - the vitriol was very nasty.

Chris

 

I find the recommendation of an 80km/h limit on rural roads horrifying. Can
you just imagine all the drivers nodding off to sleep on a long journey?
The frustration and fatigue is bad enough travelling from Cairns to
Townsville at 100km/h. 80 would be mind-numbingly boring. These simplistic
approaches to road safety do immense injustice to the complexity of road
safety and the cause of accidents.
Simon

 

In aus.motorcycles on Thu, 08 Jan 2004 12:47:48 GMT

especially as at least one study that recommended that was really just
restating the 85th percentile in absolute terms.

That is, they studied a bunch of winding roads, decided that some people
crashed on them because they couldn't work out how fast to go, and said
"set the limit at 80" instead of "set the limit at the speed that about
85% of the traffic goes at", even though that's how the 80 nwas arrived
at. Then generalised to "rural roads".

Zebee

 

Just as a converse to that, in victoria the great ocean road is
signposted at 100kph, the rural default, which could give people the
impression that 100kph is safe on that road and give them confidence
to drive beyond their ability.

Which is pretty silly given that roads ability to take life,
particularly the lives of motorcyclists, due in part to its ever
changing surface and unpredictable nature.


OK OK, I *know* that everyone here would find 100 on the GOR well
within their ability, and there is so much traffic on the GOR these
days that its a mute point. Still 100kph is a silly limit when traffic
never moves much faster than 80, and usually at 60.


Tim.

 

If you've got the impression that it's safe to do 100 just
because it's zoned 100, you're a dead man rolling anyway.

-----sharks