Superb Article by Paul Smith on Scameras in MCN
Discussion
Best article I've seen in a long time spelling out why the current Scamera policy is nonsense. The national daily papers would do well to copy.
Motorcycle news article available as two PDF files:
www.safespeed.org.uk/rules001.pdf
and
www.safespeed.org.uk/rules002.pdf
Motorcycle news article available as two PDF files:
www.safespeed.org.uk/rules001.pdf
and
www.safespeed.org.uk/rules002.pdf
Godfrey H said:
Best article I've seen in a long time spelling out why the current Scamera policy is nonsense. The national daily papers would do well to copy.
Thank you kind sir. However I didn't write the article, Rich Beach on the MCN news desk wrote most of it I believe. However, I did discover the flaw in the rules.
There's also a new Safe Speed page on the subject:
www.safespeed.org.uk/rules.html
Best Regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
This is great stuff. Wouldn't it be a good idea to e_mail it to every newspaper?
The trouble with the argument is, not that there is a flaw in the argument, but that revenue camera supporters and the control freaks in general I believe think very simplistically.
They think no further than "going slower must be safer" and "just follow the rules and you won't get caught".
That sort of person will simply not understand what 85th percentile etc etc means and when they see a graph their eyes will glaze over because the last time they saw a graph was on a teacher's distant blackboard from the back of the classroom at junior school.
The trouble with the argument is, not that there is a flaw in the argument, but that revenue camera supporters and the control freaks in general I believe think very simplistically.
They think no further than "going slower must be safer" and "just follow the rules and you won't get caught".
That sort of person will simply not understand what 85th percentile etc etc means and when they see a graph their eyes will glaze over because the last time they saw a graph was on a teacher's distant blackboard from the back of the classroom at junior school.
james_j said:
This is great stuff. Wouldn't it be a good idea to e_mail it to every newspaper?
Done that. A Safe Speed PR went out to 800 journalists and editors at 6am today.
www.safespeed.org.uk/pr105.html
Best Regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
>> Edited by safespeed on Wednesday 28th January 07:19
Nicely argued. Its a an analysis that proves what seems glaringly obvious to me, and every other competent driver:
As the road hazards become more frequent speed has to reduce to maintain safety. As the frequency of road hazards decrease its is therefore safe to go faster. Putting cameras where it is safe to travel quickly will catch competent, safe, ordinary drivers. Putting cameras where it is dangerous to travel quickly would catch nutters. But they don't put them there.
Did I understand the gist properly, Paul?
>> Edited by Don on Wednesday 28th January 07:19
As the road hazards become more frequent speed has to reduce to maintain safety. As the frequency of road hazards decrease its is therefore safe to go faster. Putting cameras where it is safe to travel quickly will catch competent, safe, ordinary drivers. Putting cameras where it is dangerous to travel quickly would catch nutters. But they don't put them there.
Did I understand the gist properly, Paul?
>> Edited by Don on Wednesday 28th January 07:19
A quick search on "85 percentile speed cameras" produced a number of 'hits'. Among them:
Can anyone say whether Wigan (and by implication the Gtr M/cr SP) are following this?
Does it only apply to "Cost Recovery" schemes?
Streaky
>> Edited by streaky on Wednesday 28th January 08:08
Hampshire CC said:Pity they don't appear to follow it though. And there are some "get out" clauses buried in the weasel words.
www.hants.gov.uk/scrmxn/c27361.html
A survey of traffic speeds should indicate whether a lower limit will, in the absence of regular enforcement, or additional engineering measures, be likely to result in lower actual speeds. Guidance, based on national experience, is that if the observed 85 percentile speed is within 7 miles per hour or 20% of the proposed limit, the limit is likely to be effective. Local speed limits are normally unnecessary where the character of the road itself limits the speed of most vehicles (say 95%) to a level at or below that of the limit under consideration.
Accidents and road safety concerns will remain key factors in determining the necessity of imposing a limit, but if all other conditions are satisfied, the lack of an accident history will not in itself rule out introducing a limit. Mandatory speed limits are not generally the solution to the problem of isolated hazards, such as at a single road junctions or bends, as they are difficult to enforce over such a short length. Other measures such as warning signs or improvements to the road geometry, lighting or footway provisions are likely to be more effective and will be considered by the County Council where the casualty record justifies such measures.
Wigan MBC said:
http://formby.wiganmbc.gov.uk/pub/council/agendas200203/environment/190203/report15.htm
"5.2 Entry into Cost Recovery will impose defined criteria for introducing new fixed and mobile safety camera sites, if they are to be included within Cost Recovery. The main criteria for introducing new sites and maintaining existing sites are as follows:
- For new static speed cameras there needs to be at least 4 Killed or Seriously Injured Accidents per km and at least 8 Injury Accidents per km in the last 3 years.
- For mobile speed cameras there needs to be at least 2 Killed or Seriously Injured Accidents per km and at least 4 Injury Accidents per km in the last 3 years.
- For red-light cameras there needs to be at least 2 Killed or Seriously Injured Accidents and at least 4 Injury Accidents at the junction in the last 3 years.
- For existing sites to be included in the netting-off process, they need only meet 50% of the accident requirements stated above.
"
- At new or existing fixed and mobile speed camera sites the 85th percentile speed of traffic must be above the Association of Chief Police Officers (ACPO) guidelines and at least 20% of drivers are exceeding the speed limit. Also, the causation factors for the majority of accidents needs to include excessive speed.
Can anyone say whether Wigan (and by implication the Gtr M/cr SP) are following this?
Does it only apply to "Cost Recovery" schemes?
Streaky
>> Edited by streaky on Wednesday 28th January 08:08
streaky said:
A quick search on "85 percentile speed cameras" produced a number of 'hits'. Among them:
Hampshire CC said:
www.hants.gov.uk/scrmxn/c27361.html
A survey of traffic speeds should indicate whether a lower limit will, in the absence of regular enforcement, or additional engineering measures, be likely to result in lower actual speeds. Guidance, based on national experience, is that if the observed 85 percentile speed is within 7 miles per hour or 20% of the proposed limit, the limit is likely to be effective. Local speed limits are normally unnecessary where the character of the road itself limits the speed of most vehicles (say 95%) to a level at or below that of the limit under consideration.
Accidents and road safety concerns will remain key factors in determining the necessity of imposing a limit, but if all other conditions are satisfied, the lack of an accident history will not in itself rule out introducing a limit. Mandatory speed limits are not generally the solution to the problem of isolated hazards, such as at a single road junctions or bends, as they are difficult to enforce over such a short length. Other measures such as warning signs or improvements to the road geometry, lighting or footway provisions are likely to be more effective and will be considered by the County Council where the casualty record justifies such measures.
Pity they don't appear to follow it though. And there are some "get out" clauses buried in the weasel words.
Wigan MBC said:
http://formby.wiganmbc.gov.uk/pub/council/agendas200203/environment/190203/report15.htm
"5.2 Entry into Cost Recovery will impose defined criteria for introducing new fixed and mobile safety camera sites, if they are to be included within Cost Recovery. The main criteria for introducing new sites and maintaining existing sites are as follows:
- For new static speed cameras there needs to be at least 4 Killed or Seriously Injured Accidents per km and at least 8 Injury Accidents per km in the last 3 years.
- For mobile speed cameras there needs to be at least 2 Killed or Seriously Injured Accidents per km and at least 4 Injury Accidents per km in the last 3 years.
- For red-light cameras there needs to be at least 2 Killed or Seriously Injured Accidents and at least 4 Injury Accidents at the junction in the last 3 years.
- For existing sites to be included in the netting-off process, they need only meet 50% of the accident requirements stated above.
"
- At new or existing fixed and mobile speed camera sites the 85th percentile speed of traffic must be above the Association of Chief Police Officers (ACPO) guidelines and at least 20% of drivers are exceeding the speed limit. Also, the causation factors for the majority of accidents needs to include excessive speed.
Can anyone say whether Wigan (and by implication the Gtr M/cr SP) are following this?
Does it only apply to "Cost Recovery" schemes?
Streaky
>> Edited by streaky on Wednesday 28th January 08:08
A Google search using just, "85th percentile speed" shows research from all over the world confirming Mr Smith's analysis though I was not aware the cameras can only be placed where the limit is below the 85th percentile as reported in MCN. Where does this information come from Paul?
Did a bit of Googling just now and found the counter-argument to this theory:
Isn't there an element of truth in this? Whatever the speed limit is, anyone varying from the speed that the majority drive at will be more likely to be involved in a collision?
The effect of placing cameras in an area will have the effect of slowing many drivers down with the effect of moving the 85th Percentile. It would not therefore necessarily increase the crash risk.
hwysafety.org said:
9. How are speed limits established? Speed limits are typically set based on a roadway's design -- for example, whether it is a narrow two-lane road or a modern controlled access freeway -- and whether the surrounding area is urban, suburban, or rural. It has been argued that measuring the speed distribution of a roadway and then setting the speed limit so that 85 percent of motorists would be in compliance reduces the need for enforcement and, at the same time, reduces crash risk by narrowing variation among vehicle speeds. However, numerous studies of travel speeds on rural interstate highways have shown that 85th percentile speeds increased when speed limits were raised to 65 mph and then continued increasing. The 85th percentile is not a stationary point. It is rather a moving target that increases when speed limits are raised. If speed limits are raised to meet a current 85th percentile speed, a higher new 85th percentile speed will soon result.
Others claim that, because interstate highways meet rigid design standards for sight distance and roadway geometry, they should be posted at their design speeds. The problem is that a design speed is not necessarily a safe travel speed. The American Association of State Highway and Transportation Officials defines design speed as "the maximum safe speed that can be maintained…when conditions are so favorable that the design features govern." In other words, it is the maximum speed at which drivers can maintain a safe level of vehicle control on a particular section of highway under the conditions for which the highway was designed. Speed limits are set somewhat lower because conditions are not always favorable and design features do not always warrant higher speeds. Many motorists also assume there is a kind of built-in tolerance factor in speed limit enforcement, so they exceed the limit regardless of what it is.
10. Does research show that slightly faster speed limits would reduce crashes? No. Advocates of higher speed limits have claimed that research on speed variation indicates faster speeds are not hazardous. They cite David Solomon's research from the mid-1950s and similar studies that seem to show an increase in crash likelihood among drivers traveling slower than the average speed and a minimum of crashes at 5-10 mph above the average speed. However, the crash-involved drivers in these studies reported their travel speeds. It is well known that drivers exceeding speed limits are likely to deliberately underestimate their speeds. Such underestimation can account for much of the apparent underinvolvement of moderately high-speed drivers in crashes. In addition, later research found that simply removing the crashes involving intersections and turning maneuvers eliminated the exaggerated overinvolvement of slower drivers in crashes. More important, the Solomon research addressed only speed variation, not speed limits. Raising speed limits raises average speeds as well.
Isn't there an element of truth in this? Whatever the speed limit is, anyone varying from the speed that the majority drive at will be more likely to be involved in a collision?
The effect of placing cameras in an area will have the effect of slowing many drivers down with the effect of moving the 85th Percentile. It would not therefore necessarily increase the crash risk.
PetrolTed said:
Isn't there an element of truth in this? Whatever the speed limit is, anyone varying from the speed that the majority drive at will be more likely to be involved in a collision?
The effect of placing cameras in an area will have the effect of slowing many drivers down with the effect of moving the 85th Percentile. It would not therefore necessarily increase the crash risk.
I don't have time to go into this in massive detail just now (although I'd like to).
Two issues:
Does changing the speed limit alter the speed of traffic? Not to any significant degree without enforcement, no. With enforcement, we all know that traffic speed can be altered. However, there's no evidence to show that this is a good thing.
Is the accident risk curve U shaped? Yes, it bloody is. Just ask yourself about the crash risk affecting a driver at 20mph in L3 of a motorway, and yu'll see for sure that a driver in the stream of traffic at a low speed has an elevated crash risk. The explanation for the disparity of results is on the following Safe Speed page:
www.safespeed.org.uk/speedlimits.html
Best Regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
Paul,
Am I correct in interpreting the article as suggesting that putting cameras in will move move people into the danger zones of the curve?
If that's the assumption then I'm not sure it's one that stands up to scrutiny. (I'm all for insisting cameras are used only where approrpiate, I'm perplexed by the argument being put forward here).
Am I correct in interpreting the article as suggesting that putting cameras in will move move people into the danger zones of the curve?
If that's the assumption then I'm not sure it's one that stands up to scrutiny. (I'm all for insisting cameras are used only where approrpiate, I'm perplexed by the argument being put forward here).
PetrolTed said:
Paul,
Am I correct in interpreting the article as suggesting that putting cameras in will move move people into the danger zones of the curve?
I'm afraid that MCN did mention that. But it's rubbish.
PetrolTed said:
If that's the assumption then I'm not sure it's one that stands up to scrutiny. (I'm all for insisting cameras are used only where approrpiate, I'm perplexed by the argument being put forward here).
It's hard to know which part of the argument you don't understand. Have you read the new Safe Speed page:
www.safespeed.org.uk/rules.html ?
If that doesn't work, feel free to give me a ring.
Best Regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
PH, what an excellent site! Where else can you find pro motoring/enthusiastic driver type people questioning an anti camera viewpoint?
If this was a t2000 or ssi forum theyd never dare to question the info the way Ted has!
Theyd be busy swalling hook line and sinker abything that put their cause in a good light and rejecting all that didnt, even if it was true!
I like it, it shows that far from being speed maddened loons tazzing around killing sweet sprogs(
), that we're actually checking out the validity of information presented to us and verifying it!
A far cry from some other people i could mention....(they know who they are)......
If this was a t2000 or ssi forum theyd never dare to question the info the way Ted has!
Theyd be busy swalling hook line and sinker abything that put their cause in a good light and rejecting all that didnt, even if it was true!
I like it, it shows that far from being speed maddened loons tazzing around killing sweet sprogs(
), that we're actually checking out the validity of information presented to us and verifying it! A far cry from some other people i could mention....(they know who they are)......
Maybe my memory is incorrect but I always understood that the 85th percentile speed is the one below which 85% of drivers travel given no other constraint.
Depends what you mean by "no other constraint" surely.
ie is a speed limit a constraint in this sense?
for example obviously it would be crazy to measure the 85th on a road at rush hour.
but when the road is clear of other traffic? Then the set limit comes into play for the majority of drivers and is an influencing factor in the results.
Perhaps some of our elder or retired b-i-b might like to comment as I'm sure they have done these measurements in the past and reported accordingly.
Equally do today's b-i-b ever get asked to do this?
Depends what you mean by "no other constraint" surely.
ie is a speed limit a constraint in this sense?
for example obviously it would be crazy to measure the 85th on a road at rush hour.
but when the road is clear of other traffic? Then the set limit comes into play for the majority of drivers and is an influencing factor in the results.
Perhaps some of our elder or retired b-i-b might like to comment as I'm sure they have done these measurements in the past and reported accordingly.
Equally do today's b-i-b ever get asked to do this?
Flat in Fifth said:
Maybe my memory is incorrect but I always understood that the 85th percentile speed is the one below which 85% of drivers travel given no other constraint.
Depends what you mean by "no other constraint" surely.
ie is a speed limit a constraint in this sense?
for example obviously it would be crazy to measure the 85th on a road at rush hour.
but when the road is clear of other traffic? Then the set limit comes into play for the majority of drivers and is an influencing factor in the results.
Perhaps some of our elder or retired b-i-b might like to comment as I'm sure they have done these measurements in the past and reported accordingly.
Equally do today's b-i-b ever get asked to do this?
"Other constraints" doesn't include posted limits.
It refers to the presence of pedestrians, junctions, curves, tops of hills, other road users etc.
Here are some links to peep at.....
www.sense.bc.ca/disc/disc-08.htm
www.dma.org/~ganotedp/85th.htm
ans www.motorists.com/mi/85th.html
deltaf said:
PH, what an excellent site! Where else can you find pro motoring/enthusiastic driver type people questioning an anti camera viewpoint?
The difference is we have nothing to hide. Absolutely nothing.
Best Regards,
Paul Smith
Safe Speed
www.safespeed.org.uk
That is absolutely fantastic Paul. It PROVES what every good driver knows intuitively but cannot voice.
I hope you get the media coverage you deserve. The two pictures alone would leave the anti-speed brigade utterly stumped.
If I was you I'd offer a cut-down version, without the stats for the mass media.
Just list the 85th percentile speeds for each of the pictures in the article, and simply state that the rules insist it's that way round; i.e. cameras only allowed on long straight roads, but not villages: please take pains to highlight the presence of kiddies in the village pic...
My Dear Ol' Mum was speachless when I showed her.
Keep up the good work!
>> Edited by _Al_ on Wednesday 28th January 22:16
I hope you get the media coverage you deserve. The two pictures alone would leave the anti-speed brigade utterly stumped.
If I was you I'd offer a cut-down version, without the stats for the mass media.
Just list the 85th percentile speeds for each of the pictures in the article, and simply state that the rules insist it's that way round; i.e. cameras only allowed on long straight roads, but not villages: please take pains to highlight the presence of kiddies in the village pic...
My Dear Ol' Mum was speachless when I showed her.
Keep up the good work!
>> Edited by _Al_ on Wednesday 28th January 22:16
Some mad geeza said:
The 85th percentile is not a stationary point. It is rather a moving target that increases when speed limits are raised. If speed limits are raised to meet a current 85th percentile speed, a higher new 85th percentile speed will soon result.
By that reckoning if the speed limit was 150mph, then all the cars will be doing 150mph... Durrrrrrrrrrrrr!!!
>> Edited by pwig on Thursday 29th January 02:13
Gassing Station | Speed, Plod & the Law | Top of Page | What's New | My Stuff