Helicopter on A40 for collision within average speed cameras
Discussion
The A40 was closed West-bound today following a collision. The air ambulance was brought in and landed on the A40 near the Polish memorial. Witnesses suggested there might have been someone receiving medical attention but, not being able to see a motorbike, have thought that one possibility is that a pedestrian was trying to cross the A40.
Some colleagues have said that, in decades travelling the A40, they have never known the A40 closed due to a collision, others have said they've experienced closure due to a collision once before. No-one has heard of the air ambulance landing on the A40 before.
This potentially major incident has occurred within a month of the new average speed cameras going live on 26th October 2015. Did the speed cameras contribute to this incident? The problem is that we may never know because TfL (Transport for London) did not run their new average speed cameras within scientific trials.
Let's hope everyone involved in the collision survives and recovers.
Some colleagues have said that, in decades travelling the A40, they have never known the A40 closed due to a collision, others have said they've experienced closure due to a collision once before. No-one has heard of the air ambulance landing on the A40 before.
This potentially major incident has occurred within a month of the new average speed cameras going live on 26th October 2015. Did the speed cameras contribute to this incident? The problem is that we may never know because TfL (Transport for London) did not run their new average speed cameras within scientific trials.
Let's hope everyone involved in the collision survives and recovers.
TwigtheWonderkid said:
Wow!
All we know is that there has been an accident on the A40, and you've jumped to asking if the newly installed av. speed cameras are to blame. Just wow.
And by the way, I live in W London close to the A40 and over the years it's been shut numerous times following bad accidents.
Well of course. If the authorities had done their job properly in the first place then others would not need to investigate. We know that fatal and serious collisions increased following the deployment of mobile speed cameras in Thames Valley. We also know that fatal and serious collisions increased following the installation of fixed speed cameras in Thames Valley. It may well be that average speed cameras also result in increases in fatal and serious collisions but, since none have been installed within scientific trials, how will we know? If TfL are attempting to deceive people with their current speed cameras, why would they suddenly start being honest with their new average speed cameras?All we know is that there has been an accident on the A40, and you've jumped to asking if the newly installed av. speed cameras are to blame. Just wow.
And by the way, I live in W London close to the A40 and over the years it's been shut numerous times following bad accidents.
We here have known the A40 to be shut due to works, and to have delays due to lane closures following collisions, but we've very rarely, if ever, known the A40 to be completely shut due to a collision. Can you confirm that the A40 was definitely completely "shut numerous times" due to collisions, and not simply backed up with only 1 lane open, or shut due to works?
TwigtheWonderkid said:
Dave Finney said:
Can you confirm that the A40 was definitely completely "shut numerous times" due to collisions, and not simply backed up with only 1 lane open, or shut due to works?
Last October it was shut following a fatality at Swakeley roundabout. A few years back a plane overshot the runway at Northolt and it was closed. It was shut about 2 yrs ago when a cyclist was killed, again on the stretch by Northolt Airport. It was shut a few months back between Loudwater and High Wycombe due to a vehicle fire. I work in Bucks and live in London. I use it, against the flow, every day. It's been completely shut many times over the years, and I've had to divert.http://www.getwestlondon.co.uk/news/west-london-ne...
Thanks TWK but I was thinking of examples where the A40 was completely closed due to a collision within what is now the average speed camera system, all your examples are outside the average speed camera system and none of them near where you live. So have you also never experienced the A40 was completely closed due to a collision from the Polish to the end of the raised section?
TooMany2cvs said:
I'm actually quite intrigued as to how 50mph average speed cameras on a dual carriageway can cause a collision bad enough to need an air ambulance. Perhaps somebody could explain...?
You are joking, aren't you? Speed cameras may introduce many factors that could contribute to collisions including sudden braking, bunching, distraction, tiredness, and that's not even considering the reduction in Traffic Police to pay for them.tuffer said:
GPSHead said:
tuffer said:
A speed camera of any type has never caused an accident. a driver reacting badly to seeing a speed camera on the other hand.....
You could make a similar argument about people who drive at 10mph on motorways and dual carriageways. They're not going to cause many collisions themselves at that sort of speed, but why introduce something that is going to create a risk of drivers "reacting badly", unless it can be shown to have benefits that outweigh that risk?(And, as has been pointed out in this thread, TfL etc don't seem too keen to attempt to ascertain the actual benefits of cameras, almost as though they're afraid that any such study would produce the "wrong" results...I'm really glad that people with that sort of attitude are in charge of our road safety!)
tapereel said:
TwigtheWonderkid said:
CGJJ said:
"I've seen a deer on the road at Hanger Lane".
Best post ever in support of average speed cameras.
Daftest post considering I don't support average speed cameras. I just don't support stupid, brain dead and downright lazy arguments against them. It's the idiots with their rubbish arguments against that make the job so easy for the pro speed camera lobby.Best post ever in support of average speed cameras.
Either the facts are supported by the ubiquitous conclusion or the contra view is usually taken by cranks. Reports that conclude against the support for traffic regulation are not challenging...so far.
We know KSI have reduced at speed camera sites, but we also know that the reduction was not caused by the speed cameras. The primary reason that KSI have reduced has been the "site-selection" effect (often referred to as "regression towards the mean") yet no official report has managed to either measure this effect, or to fully exclude it from their final results. The effect of speed cameras, therefore, has not been established in official reports.
Independent reports, OTOH, have managed to produce results that do not contain any site-selection effects. They found that the entire KSI reduction was due to the effect of site-selection and that there was no KSI reduction after speed cameras were deployed.
Right now, therefore, the most accurate evidence available suggests speed cameras do not save lives, and do not prevent serious injuries.
It's a sad reflection of modern political Britain that we now have a "pro speed camera lobby" and an "anti speed-camera lobby". Why can't citizens be independent, unbiased and simply examine the evidence?
vonhosen said:
Dave Finney said:
tapereel said:
TwigtheWonderkid said:
CGJJ said:
"I've seen a deer on the road at Hanger Lane".
Best post ever in support of average speed cameras.
Daftest post considering I don't support average speed cameras. I just don't support stupid, brain dead and downright lazy arguments against them. It's the idiots with their rubbish arguments against that make the job so easy for the pro speed camera lobby.Best post ever in support of average speed cameras.
Either the facts are supported by the ubiquitous conclusion or the contra view is usually taken by cranks. Reports that conclude against the support for traffic regulation are not challenging...so far.
We know KSI have reduced at speed camera sites, but we also know that the reduction was not caused by the speed cameras. The primary reason that KSI have reduced has been the "site-selection" effect (often referred to as "regression towards the mean") yet no official report has managed to either measure this effect, or to fully exclude it from their final results. The effect of speed cameras, therefore, has not been established in official reports.
Independent reports, OTOH, have managed to produce results that do not contain any site-selection effects. They found that the entire KSI reduction was due to the effect of site-selection and that there was no KSI reduction after speed cameras were deployed.
Right now, therefore, the most accurate evidence available suggests speed cameras do not save lives, and do not prevent serious injuries.
It's a sad reflection of modern political Britain that we now have a "pro speed camera lobby" and an "anti speed-camera lobby". Why can't citizens be independent, unbiased and simply examine the evidence?
It's looking at speed limits that matters.
If we have speed limits, we have to accept enforcement & consequences of that enforcement.
The question therefore is about the benefits of speed limits over & above any consequences of their enforcement.
No benefit, no enforcement, because there'd be no speed limits to enforce.
1) self enforced
2) enforced by Police
3) enforced by speed camera
4) other (CSW etc)
Each type of speed enforcement may have different effects and we can have a little, lots or none of each.
We know that self enforcement definitely occurs. When speed limits are changed by 10mph, average speeds change by 1-3 mph. This has been done thousands of times and the results are consistent. And this is without any change in enforcement levels.
When Police enforce motoring laws they will include speeding but they tend to prosecute when the speed is unreasonable for the conditions or when associated with other infringements, IOW: when it is in the public interest to do so.
Enforcement by speed camera is fundamentally different to the two above. Prosecutions are pursued whether in the public interest or not, there have never been any scientific trials, the most accurate evidence suggests that they do not save lives or prevent serious injuries, the authorities have deceived the British public about the effects of speed cameras and we've had to reduce Police numbers because of the cost to society of running speed cameras.
We need two things from the authorities:
1) honesty
2) speed cameras deployed within scientific trials (the best quality evidence)
The problem is that we have not had either of these for over 20 years now. Time for change.
Devil2575 said:
Dave Finney said:
Independent reports, OTOH, have managed to produce results that do not contain any site-selection effects. They found that the entire KSI reduction was due to the effect of site-selection and that there was no KSI reduction after speed cameras were deployed.
Care to link to these reports?http://speedcamerareport.co.uk/08_mobile.htm
This was the second report to have fully excluded the effect of site-selection from the final results:
http://speedcamerareport.co.uk/09_fixed.htm
Devil2575 said:
Dave Finney said:
Devil2575 said:
Dave Finney said:
Independent reports, OTOH, have managed to produce results that do not contain any site-selection effects. They found that the entire KSI reduction was due to the effect of site-selection and that there was no KSI reduction after speed cameras were deployed.
Care to link to these reports?http://speedcamerareport.co.uk/08_mobile.htm
This was the second report to have fully excluded the effect of site-selection from the final results:
http://speedcamerareport.co.uk/09_fixed.htm
I found this report...
http://www.racfoundation.org/assets/rac_foundation...
In the first 3 NSCP reports, the authorities tried to claim that site selection had no effect at all but, in the 4th, they estimated that site selection might be a larger influence on KSI rates than all other factors combined.
What you've found is Professor Allsop's 2010 report for the RAC Foundation, which I think was the authorities 2nd attempt at estimating site selection effects (or RTM). You'll notice that the method used is in 2 parts, the 1st part could have been accurate but the actual SSP has since been found to be substantially longer than was assumed. The 2nd part is a model that turns out to be incorrect for speed cameras.
As accuracy has increased, site selection has been found to have a greater influence than was first thought. When site selection was eventually measured, it was found to be responsible for the entire KSI reduction, with the speed cameras not demonstrated to have saved any lives, and not demonstrated to have prevented any serious injuries.
There is an easy solution: run speed cameras within simple scientific trials.
Devil2575 said:
Pete317 said:
Now that you've gotten that out of your system...
What do you want me to say?One report is written by a respected academic qualified in the subject matter and the other reports are written by someone who has set up a website.
Forgive me for giving more credence to one than the others.
1) believe what the authorities tell us
2) examine the evidence
As we rarely have the time to take option 2, we usually take option 1. The hope is that we would have reached the same conclusion from option 2 anyway but, as numerous events and scandals demonstrate, this is not always the case.
In the case of speed cameras:
2008: I developed and published my "Four Time Period" method
2010: Professor Allsop published his 1st report for the RAC Foundation
2012: I published the 1st report using my "Four Time Period" method (http://speedcamerareport.co.uk/08_mobile.htm)
2013: Professor Allsop recommended that researchers use my "Four Time Period" method
2013: The DfT and the RAC Foundation endorse my "Four Time Period" method
So there is much more agreement than some might suggest!
Is it possible to have an intelligent, grown-up debate about speed cameras? I am determined to believe that it is.
What I actually wrote was: "Some colleagues have said that, in decades travelling the A40, they have never known the A40 closed due to a collision, others have said they've experienced closure due to a collision once before. No-one has heard of the air ambulance landing on the A40 before."
I have campaigned for speed cameras. Some years ago when it looked as though many speed cameras might be removed, I campaigned for as many as possible to remain within a scientific trial. When TfL decided to trial average speed cameras, I campaigned for their average speed cameras to be installed within a scientific trial. Let's use speed cameras, but we need to know what effect they're having and, since the authorities have been unable to determine their effect, this must be done within scientific trials.
When we have speed cameras deployed within scientific trials, we will finally have the evidence upon which to base a valid judgement.
http://speedcamerareport.co.uk/02_scientific_trial...
What I actually wrote was: "Some colleagues have said that, in decades travelling the A40, they have never known the A40 closed due to a collision, others have said they've experienced closure due to a collision once before. No-one has heard of the air ambulance landing on the A40 before."
I have campaigned for speed cameras. Some years ago when it looked as though many speed cameras might be removed, I campaigned for as many as possible to remain within a scientific trial. When TfL decided to trial average speed cameras, I campaigned for their average speed cameras to be installed within a scientific trial. Let's use speed cameras, but we need to know what effect they're having and, since the authorities have been unable to determine their effect, this must be done within scientific trials.
When we have speed cameras deployed within scientific trials, we will finally have the evidence upon which to base a valid judgement.
http://speedcamerareport.co.uk/02_scientific_trial...
Devil2575 said:
Devil2575 said:
When I get a chance I'll read the reports and let you know what I think. I currently don't have time.
Ok, so I've read some of the stuff. There's a lot to get through and I have limited time.I have a few observations.
1) I understand the concept of RTM and I understand the example used to demonstrate it's effect. However the usefulness of the Oxbube example is only to demonstrate the concept, because it is by design simply random numbers. Actual road traffic accidents are not simply random. There is a random element to them but aspects will influence the probability of an accident occurring.
2) You said If the start and end of the SSP for every site within the analysis can be aligned, a graph should show a sudden (vertical) change in the collision rate at the start of the SSP, and another sudden (vertical) change at the end. This should prove (as far as is possible) that this was indeed RTM and not something else.
3) Why? You are assuming that a camera site is only selected when there is a period of above average accidents. Also even if this is the case there is no guarantee that there would be a vertical change at the start and the end. While it is probable that events regress towards the mean, it is not a certainty at all. Just because I have rolled 3 sixes doesn't mean that I definitely won't roll another 6. With a large number of rolls it is inevitable but with only another few it is entirely possible.
4) You have set the criteria that you need to positively identify the period of the SSP, which you base on clearly observing a sudden rise and fall. You have then gone on to exclude all those sites where you can not positively do this. The problem with this is that you have actually cherry picked the data which you are going to accept. You have been working under the false impression that the data within the SSP will automatically be above average and be bounded by a sudden rise and fall as well as the notion that the data in both the pre SSP and the ASBiC periods will be representative of the mean. If the pre SSP and ASBiC periods is a large enough dataset then you can work on the assumption that it will be average, but is this case is that genuinely the case? How many years of data did you actually have? I have had a look at some of the links but can't find this data. I may have missed it however, it's just not clear where it is.
It could actually be the case that the sites where you were able to observe this sudden change at either end of a period you have assumed to be the SSP are actually showing a lower than average accident rate over the pre SSP and ASBiC. This means that you are adjusting for the RTM based on an incorrect mean.
5) Also don't forget that the years you are stating are the SSP due to being above average are actually still part of the average. By removing them from the data you could be reducing the average value. Again, with a big enough data set for pre SSP and ASBiC this will not be the case, or at least it will not be significant. But imagine having data on 20 rolls of a dice then removing a run of 3 sixes from the data. The average number from rolling a dice is 3.5. So assuming over 20 rolls you get the average, then the total will be 70. Remove 18 from this to account for 3 sixes then divide by 17 and you get 3. You are now working under the assumption that 3 is the average from rolling a dice, but it isn't.
6) I do accept that the best way to determine the effectiveness of speed cameras would be to do a randomised trial, I just don't accept that your method tells us anything due to the fact that you have selelcted the data to which you are going to pay attention based on false assumptions.
I've numbered your paragraphs above:
1) yes, the Oxbube example is only to demonstrate the concept
2) yes.
3a) there isn't any assumption that a camera site is only selected following an above average number of accidents. If the data shows all of the characteristics of the Oxbube example, then we can deduce that the sites within the analysis were "often" chosen following an above average number of accidents. In the case of the mobile speed camera sites, many (12 I think) were chosen following no accidents at all in the SSP. Even including those sites, the data still shows the SSP clearly.
3b) It is true that "Just because I have rolled 3 sixes doesn't mean that I definitely won't roll another 6" but, if you choose 75 dice that have each just rolled 3 sixes, it is extremely unlikely that all of them will roll 3 sixes again at the same time (equally likely they will all roll 3 ones at the same time).
4) If I had done what you say you would be right. "Cherry picking" the data in the way you describe would likely produce unreliable results, but that's not what I did.
Find figure 8.1 here: http://speedcamerareport.co.uk/08_mobile.htm
Figure 8.1 shows the data at ALL qualifying sites, none were excluded (qualifying sites are all mobile speed camera sites that were active in Thames Valley at the start of 2009 and that had been operating for 3 or more years).
The SSP was determined by examining the data for all sites together (not each individually).
5) yes that's true, but what that does is introduce another selection effect. The FTP method removes the effect of site-selection. You're right that the average may be higher than the "mean", that's what the site-selection process can do. The "mean average" can be different to the "mean (normal or expected value of a random variable)". Who was it that decided to use the same words for different things!?!
6) Mathematicians have told me that my FTP method is nothing new, it's been basic mathematics for decades. I get both sides, one side says it's obvious and nothing new, the other says it doesn't work. In the end there are 2 conclusions:
a) the entire KSI reduction at these sites had already occurred a full year before the mobile speed cameras were deployed.
b) whatever opinions people have, all doubts could be settled by running simple scientific trials
Devil2575 said:
Have you got a link to the actual data you used? Is it all contained within an individual excel spreadsheet for example?
You're asking all the right questions, you must be an engineer! Before believing a report's conclusions, readers should evaluate the data source and understand the methods used.Yes, an excel spread sheet (called "mobile cameras TVSRP.xls") containing the data used in the report is in the "Supplementary information" at the end of this page:
http://speedcamerareport.co.uk/08_mobile_refs.htm
The "Supplementary information" also has a sample extract from the full database that was created and supplied by TVSRP (Thames Valley Safer Roads Partnership).
Interestingly, I asked a similar question when the RAC Foundation report that you mentioned was published. The evaluation of RTM in that report starts with data from 6 partnerships in Table 5 (p31/58, labelled p20). I asked which partnerships supplied that data but was told that the data source must remain secret because the partnerships only released the data on the understanding that they would not be identified.
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