Safe Speed Forums

RTTM is still valid.


Maybe you should have done the obvious: Link

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

lol, i found that ages ago, i had to read it twice before i saw RTM



sunflower seeds springs to mind immediately

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now retired

If I can pick you up on several little things:


So yes, accounting for "long term-trend" still leaves RTTM unaccounted for, but even then RTTM is still the majority cause of the KSI reduction at camera sites (not the cameras themselves) - not that this is reflected in the subsequent claims you quoted.
Do you get it now?

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

If you are still confused, or unsure, perhaps these links may help ? :
http://www.safespeed.org.uk/rttm.html
http://www.safespeed.org.uk/gambling.html
viewtopic.php?f=14&t=22901
viewtopic.php?f=8&t=2687
viewtopic.php?f=16&t=2691
viewtopic.php?f=24&t=2685
viewtopic.php?f=16&t=14073

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Safe Speed for Intelligent Road Safety through proper research, experience & guidance.

If RTTM is responsible for all or the majority of casualty reduction at fixed camera sites then we should expect that a large majority or all of the fixed camera site casualty figures have returned to or approached their pre-enforcement mean.
As the majority of fixed cameras were installed before 2003 and were based upon the collision history of the previous 4 years, a period of 8 years of RTTM benefit can be discounted by those sites returning to the mean.
As I understand it, they have not so it can be reasonably stated that action taken by inserting cameras bas benefitted safety beyond what can be expected by no such action being taken.
The RTTM argument avaunt cameras, something that in itself relied on the unknown and prediction, is now defeated by what has happened.
RTTM is dead, try something else.

The fundamental problem is that the SCPs claimed huge casualty reductions based on statistics and said that this was due to the effects of cameras. In fact, the extreme rarity of these incidents means that statistical methods cannot meaningfully be used in this analysis because of the small "population" and randomness being the predominant effect.

To turn to GS's somewhat confusing post, if RTTM were responsible for the majority of the claimed reduction in accidents then the way to prove this would be to remove all vestiges of cameras from a site(not just switch them off) and then wait and see what happens to the long term trend. This cannot have happened yet as:

- most cameras housings have not actually been removed;
- not a long enough period of time has passed to judge.

My personal recollection of a camera being installed at the infamous Whinwhistle Road junction on the A36 was that there was an accident at the spot just a few weeks after the camera was installed and two people were killed. Since then nobody has been killed. We can draw no conclusions from this as the incidents are so rare.

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Malcolm W.
The views expressed in this post are personal opinions and do not represent the views of Safespeed.

GS, you have that exactly 180 degrees the wrong way round.

The cameras were installed in response to higher than normal casualty figures.
When, as was almost guaranteed to happen, the casualty figures returned to their (lower) long-term mean, (the RTTM effect) the decrease was attributed to the cameras.
After the cameras were installed the casualty figures did not reduce to lower than normal, as you seem to be suggesting.

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Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

Yes, Pete,you are correct and once again, GS's lack off understanding, of basic maths, shows through! Obviously CSE maths or above, wasn't needed to get the job.

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My views do not represent Safespeed but those of a driver who has driven for 39 yrs, in all conditions, at all times of the day & night on every type of road and covered well over a million miles, so knows a bit about what makes for safety on the road,what is really dangerous and needs to be observed when driving and quite frankly, the speedo is way down on my list of things to observe to negotiate Britain's roads safely, but I don't expect some fool who sits behind a desk all day to appreciate that.

OK. You try this...


Had you actually understood the RTTM analysis, you would have realised that there is another generally unaccounted factor 'long-term trends'. This is primarily nation-wide safety measures such as improved occupant protection and improved post crash care. This is another confounding factor that the SCPs conveniently don't account for when making claims of camera effectiveness.


Again: long-term trends

You are another who doesn't understand the figures given in "The national safety camera programme - Four-year evaluation report (December 2005)". There does seem to be a strong correlation between those involved with camera enforcement with those who portray exaggerated claims of camera effectiveness.
Note your lack of rebuttal for each of the following (except the one where you spectacularly failed), which are a very topical reminder of exactly this issue:
viewtopic.php?f=17&t=21866&p=218634&hilit=long+term+trend#p218634
viewtopic.php?f=14&t=21388&p=215072&hilit=long+term+trend#p215072
viewtopic.php?f=14&t=21388&p=215064&hilit=long+term+trend#p215064
(all three are the most recent three occurrences where this confounding effect was pointed out to you)


You have unsuccessfully tried this on before!

Unacknowledged direct rebuttal
Unacknowledged rebuttal 2

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

Oh my god, you really genuinely do not get it do you? Could you please answer me this, are you actually purposefully misrepresenting the issue of RTTM, or do you genuinely lack the intellect to grasp the concept of the mean?

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Regulation without education merely creates more criminals.

no, i think because it is mentioned the effect has been snowballed because it was written, if local micro climate was written then that would have snowballed, similar to prior opinion

however RTTM not accounting to RTTM or as Paul used to say a random cluster of accidents, 5 years on have we reached the repetative cycle so a huge increase in accidents at camera site is due

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now retired

So the key word "without" doesn't have any impact on that sentence? Really?


Cam Op,

The effect is called "regression TO the mean", not "a cyclic deviation FROM the mean"

I find it incredible that you actually still don't understand RTTM!

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

i fully understand you can get the perfect storm syndroym, where everything is in place with tragic results,

ref the accident in north wales where a driver on bald tyres took out a group of cyclists, so many what if's in that tragic event, i cannot find the link in the cycling section, mass posts started by the swiss though, a real close family IMO,

what if the cyclists had not gone out
what if it was raining
what if the car did not have bald tyres
what if the police patrol car had stayed there until the road was salted

would that be classed as one KSI or 1 tick for each person killed or injured,



so its different from a council claiming they have kept the roads free from snow 51 weeks of the year,



just found this http://www.dsfire.gov.uk/News/Newsdesk/IncidentDetail.cfm?IncidentID=17380&siteCategoryId=3&T1ID=26&T2ID=41

http://www.dsfire.gov.uk/News/Newsdesk/IncidentDetail.cfm?IncidentID=17385&siteCategoryId=3&T1ID=26&T2ID=41


so in RTTM theory nothing should happen hear again

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now retired

... Oh I understand RTTM very well indeed.

It seems our friends here do struggle though.

While it is admitted it has an effect when year-to-year figures are used long term analysis can reveal the benefit.

The mean after treatment is now much lower than the mean before treatment and below the long term trend at most fixed sites. How can the benefit, some of it be attributed to speed management and not other effects? Simple, the speed of traffic is reduced after treatment.

When the mean changes effects beyond RTTM can be seen. If you deny that then you don't understand RTTM. It really isn't a complex concept if you have more than half a wit.

Ah yes, the Swiss, so close they could have been one fool not 3. When they said what their name was and where they lived no such person of that name lived in the county. When the Durham officer revealed his name and rank no such officer served. In Durham or earlier in Manchester. Maybe they had diplomatic immunity or perhaps were a figment of someone's imagination. How come they don't get the Internet in that part of the US. What a strange set!

Not nearly.

The RTTM conclusions indicate that it is unlikely (but not impossible) for such an accident cluster to strike again at those same locations, within the next three years, unless those locations are already having an average of such an event every three years (a genuine accident blackspot, as opposed to a location that had an infrequent/single glitch - which the SCPs like to portray as a blackspot).

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

How absolutely random!
Run out of arguments have you, RSS man? That's a bit pathetic, especially for someone of your supposed stature!

Why not tell us who you are?

viewtopic.php?p=218033#p218033

viewtopic.php?p=218459#p218459

How many multiple personas have you had on various forums? I can think of another three personas that you have had on this one alone...


Getting back on track:

Thanks to the illusion of RTTM (you hadn't actually accounted for this effect with your weasel wording)


A euphemism for "forcing adverse reactions"


More errors.

You conveniently forget the other, even more significant, confounding factor of "bias on selection". This is independent, and additional to, RTTM (and long-term effects).
In short, this is the effect of other safety measures having been placed at speed camera sites such that the accident rate regresses to below the previous mean.

'Bias on Selection' – the application of an external influence so making the 'scheme' (the camera) falsely appear to be more effective than it actually is.
(I don't know what the technical name is so I coined my own.)

When a speed camera is erected alongside another new road safety measure, like a pedestrian barrier/crossing, central reservation, junction re-layout, etc, what do you think gets credited for any subsequent reduction in accident rate? Both, or just the "camera site"? Think about that – that’s sneaky huh?

To explain: The illusion of Bias On Selection will occur when considering the effectiveness of one specific treatment at a site where multiple remedial treatments were also applied. For example, the addition of a pedestrian crossing, or changing the layout of a junction, pedestrian crossings or barriers, etc, at a camera site, will result with an additional reduction of KSI beyond that caused by the camera (if any).
Urban sites will often have multiple measures applied to a problem area. It is possible for any of these other (genuine) treatments to be placed at camera sites. TRL agree with me: "The treatment might be one of many applied at the same scheme. " (a fantastic document that demolishes the case for cameras).

The use of those other genuine safety measures within camera sites would actually be hiding any negative effect from speed cameras, even though there is a substantial KSI reduction at the sites following installation of the cameras (even when accounting for RTTM and trends), and this is exactly what we observe.
One or more of these treatments could have a positive effect on safety. However, it is possible that one of these treatments isn’t giving any benefit, or may even be having a negative effect, yet together with the genuine treatments they yields an overall net KSI reduction, thus effectively hiding the negative impact of the bad treatment.

No figures exist for the effectiveness of the described other measures, that in itself should be ringing alarm bells – yes?
So 'bias on selection' is an additional illusion of false effectiveness, independent of statistical RTTM – yes?

If you deny that, then you don't understand it.

I've beaten you on this again, and again, and again, and again. You never responded to any of those.

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

How's this for an example: At a particular site, they record 2 KSI's per year for three years. In the following year they record an uncharacteristic 6 KSI's. They then introduce a camera, and the following four years produce 2 KSI's a year, exactly the same as before.
But now do they not only claim that the 'improvement' was down to the camera, they also claim that the average before the camera was ((2+2+2+6)/4) = 3 per year, and the average after the camera was ((2+2+2+2)/4) = 2 per year, ie a 33% 'improvement', whereas the real improvement was zero.

Think about it another way as well - if there was an improvement of just 1 fatality every 2 years at each of the 6000+ camera sites, total fatalities would have reduced to zero within 1 year of the cameras being introduced. But they didn't, did they?



That presupposes that accidents are caused by speed - you still have not given a satisfactory explanation as to how.



What does that make you then?

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Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

but the links above show 2 accidents in or around the same location on two consecutive days, i initially thought the location was a very nasty stetch of the M5 where the outside lane lane merges with the third lane very suddenly, no advance warning due to the split level nature of the road, but google mapping shows the location to be a very flat straight section of motorway



where is this site

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now retired

That was a hypothetical site

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Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

thought as much, pretty pointless in posting it then

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now retired