software the safety camera partnerships claim success The rules now say that a speed camera must be sited at a location where accident figures for the last three years confirm a risk due to
2
angel road
software drivers using excess speed
Sounds good doesn`t it We`ll only be putting cameras at accident black spots then and we`ll see the benefits clearly. But there are massive problems with this approach
2
angel road
software Read on Scaring away the traffic Drivers don`t like speed cameras Some go out of their way to avoid them and use alternative routes whenever possible Others will choose a camera free route
2
angel road
software in preference to a camera infested route where similar alternatives exist It`s obvious that installing a camera will tend to scare some of the traffic away and all things being equal this will
2
angel road
software provide a potential reduction in accidents at the camera site But since the traffic tended to go elsewhere so will the accidents Often the alternative routes may be more minor roads which are
2
angel road
software more dangerous new Other improvements Sometimes a new speed camera is added to a problem area as part of a treatment scheme to reduce accidents at a genuine accident black spot The treatment
2
angel road
software scheme might include new road markings new signs and changes to a junction layout as well as a new speed limit and a speed camera The caution here is to know what parts
2
angel road
software of the treatment scheme had what effect on any resulting accident reductions In truth we`ll probably never know how much of any improvement results from which components of the treatment They`ll probably claim
2
angel road
software the entire improvement was due to the speed camera We know that any such claim is highly unlikely to be true How big is a site Recent figures we saw for claimed speed
2
angel road
software camera accident reductions included a stretch of road 2 km long Now it`s easy to imagine a dangerous stretch of road 2 km long But how much of the road would a single
2
angel road
software speed camera affect The actual area surveyed is under 50 meters allow 100m before the camera for deceleration and 100m after it and regular drivers on the route will have been affected for
2
angel road
software just 250m or 1/8th of the distance Any accident within the site but not within range of the camera will very likely be entirely unaffected by the camera
But they have the
2
angel road
software random cluster effect to fall back on Random clusters (regression to the mean) Suppose we have a county with 100 potential speed camera sites 1000 accidents in the last three years and one
2
angel road
software camera to place Now it`s extremely unlikely that all these sites have recorded similar levels of accidents There`s always a certain degree of random clustering We don`t know the maths that governs random
2
angel road
software clustering but fortunately it`s very easy to model with a bit of BASIC and some random numbers The program is below We made runs of 1000 complete simulations which average the largest cluster
2
angel road
software to get an average size of largest cluster figure Here are the results Number of Sites Number of Accidents average size of largest cluster normal average value advantage 10 1000 115 100 13%
software 665 1 85% - So we go and place the camera at the site of the largest cluster That`s the trick bit The figures for the untypical cluster are now planted in the
2
angel road
software history of the new camera Over the next time period assuming all is equal the number of accidents at the site will tend to return to average Without the camera contributing anything at
2
angel road
software all to the changes and with perfectly normal statistical averages using the original example we will be able to truthfully claim a 46% reduction in accidents at the camera site for our next
2
angel road
software press release If you could place bets with odds like these you would be on a sure fire winner Its been suggested that we could get the same effect by burying a bible
2
angel road
software at the site or putting a garden gnome at the roadside which is true if we site cameras and record results on this typical but hopelessly flawed basis The government call this effect
2
angel road
software regression to the mean and it is documented There`s even a compensatory equation (click here) do they ever use it
I suspect not External trends Often over a survey period there will
2
angel road
software have been national trends in road accidents So if a certain class of accident has gone down nationally by 5% and they claim a 4% reduction at the camera site you might reasonably
2
angel road
software guess that accidents at the camera site rose relative to the national trend In practise a small external trend reduction will probably just bolster up the usual claims by a few percent
2
angel road
software Genuine accident black spots There are undoubtedly a few accident black spots around the country where a speed camera could be justified as part of a genuine safety improvement scheme Likely candidates might
2
angel road
software be junctions on fast roads or before deceptive bends where too many drivers get it wrong In these cases the more visible the camera the better the results Huge clear signs Speed Camera
2
angel road
software Ahead together with a reminder of an appropriate speed limit for the hazard area might well produce good road safety results The camera would need to be sited on the approach to the
2
angel road
software hazard area no more than 100m from the bend or junction Such installations do exist but are very much the exception.
At a wild guess we`d estimate that considerably less than 5%
2
angel road
software of the cameras meet these sensible requirements properly Spin The so-called safety camera partnerships employ PR men or spin doctors whose job it is to ensure that the messages reaching the public are
2
angel road
software positive In many cases the public seems to buy into the lies Keep your eyes wide open for bogus claims Almost all the claims are bogus and support policies which simply don`t work
2
angel road
software to save lives
Remember that the spin people are trained to tell you something clear and believable and that when they succeed they are doing what they are paid to do If
2
angel road
software it didn`t work they wouldn`t be employed They are employed specifically to present the facts creatively to make them sound better than they are They have no moral or legal obligation to the
2
angel road
software truth Of course if accidents go down they claim it`s the cameras doing it If accidents go up they say we don`t have enough cameras drivers are still speeding we must have more
2
angel road
software cameras new Selective reporting The spin doctors love to choose the best figures and ignore the worst So if serious injuries are down by 5% (say from 1000 to 950) and deaths are
2
angel road
software up by 20% (say from 100 to 120) they might just tells us about the serious injuries or they might lump them together into that meaningless and misleading statistic Killed and seriously injured
2
angel road
software In this example KSI has dropped from 1100 to 1070 so they`ll possibly claim a 3% drop in KSI But wait What are we going to compare with what when we`re quoting changes
2
angel road
software in percent The spin doctors can cherry pick the best figure 3 year average 5 year average 1994 to 1998 average baseline Last year`s figures 1990 figures They pick whatever they want to
2
angel road
software tell the story that they want you to hear The only honest method is to show all the figures year by year Always be suspicious if they use an average figure new KSI
2
angel road
software (killed and seriously injured) KSI is always misleading for two important reasons One it carries the assumption of death onto a much larger group of serious injuries As a rule of thumb expect
2
angel road
software the killed figure to be about one tenth of the serious injury figure And two the phrase serious injury conjures up the image of a wheelchair case But here`s the definition of serious
2
angel road
software injury that`s used Serious injury An injury for which a person is detained in hospital as an in-patient or any of the following injuries whether or not they are detained in hospital fractures
2
angel road
software concussion internal injuries crushings burns (excluding friction burns) severe cuts and lacerations severe general shock requiring medical treatment and injuries causing death 30 or more days after the accident from RAGB notes
2
angel road
software So in reality many of these serious injuries will be fully healed in a week or two and many more in three months That`s not intended to lessen the human misery of the
2
angel road
software situation and some people are seriously injured with life-changing consequences But the reality is far less than it sounds The reality of 1000 KSI might often be 100 killed 100 with permanent or
2
angel road
software long term injuries and 800 walking wounded Gnomes cut crashes by 60% Since the benefits outlined here add up together we thought we`d do a worked example for the benefits of planting our
2
angel road
software large and very very ugly imaginary garden gnome at the roadside We chose a site that had five serious accidents over the last three years We placed the gnome a year ago and
2
angel road
software there`s been just one accident since Out comes the calculator and we immediately deduce that the average for the last three years was 1667 accidents Looks like we`re on a winner with our
2
angel road
software gnome Our headline is Gnomes cut crashes by 60% and we embark on a large scale gnome introduction scheme But it isn`t the truth Other effects have taken place The gnome was so
2
angel road
software large and very very ugly that 10% of traffic has diverted to other routes General road traffic accidents in the wider area have reduced by 3% perhaps due to road engineering and vehicle
2
angel road
software safety improvements We do a regression to the mean test and discover that the average number of accidents at the site is probably only 08 per year we verify this by looking back
2
angel road
software a little further in the history of the site and discover that in the previous 10 years taken as a whole there have been 9 accidents So the true score for the apparent
2
angel road
software effect of our gnome is 1 accident 90% of the previous traffic level 97% to allow for general accident reduction 0873 so we calculate that the gnome has increased likelihood of accidents by
2
angel road
software 0873/08 = 9 Of course it`s highly unlikely that figures based on a single accident have any statistical significance But we`ve invested quite a bit in the gnomes and we decide to keep
2
angel road
software quiet about it We don`t want to see the investment go to waste and if we admit that the gnome appears to have increased accidents we might lose our job
Somewhere deep
2
angel road
software in the police report for the accident at the gnome site is a statement from the driver of the crashed car saying: It`s eyes seemed to follow me and I stared at it
2
angel road
software When I looked back ahead the traffic had stopped and I couldn`t brake in time Gnomes like that shouldn`t be allowed at the road side Keeping them honest It might not be possible
2
angel road
software to keep them honest but we should be asking the following questions What are the total accident figures for the whole county How do these figures compare to national trends Will we see
2
angel road
software the benefits from the cameras reflected in the national accident statistics we haven`t yet after 10 years How many sites and how many accidents What are the traffic reductions at your camera sites
2
angel road
software What have you done to compensate for the effects of random clustersw what other safety improvement treatments were applied at the same time as the camera Together these questions should uncover most of
2
angel road
software the basic lies Introduction We are well and truly sick and tired of hearing the same old lies and misleading statements trotted out again and again and again The Scamera Partnerships apparently love
2
angel road
software the lies and we`d be surprised to find a Scamera Partnership site that didn`t contain a few of them Ask yourself Why do they need to fiddle fabricate fudge and fib The one
2
angel road
software third lie examples One third of accidents are caused by speeding Speeding kills 1100 every year One third of accidents have excessive speed as a cause or contributory factor Speed is a factor
2
angel road
software in one third of crashes Source Not known it`s probably just spin We`ve never seen any research or scientific evidence to support it Truth There`s a shortage of actual UK data published about
2
angel road
software excessive speed as an accident causation factor In the UK and in other countries it has long been the convention to gather data for accidents where the speed was excessive for the conditions
2
angel road
software without reference to the speed limit Many Police forces gather accident causation factors but few publish them in public West Midlands Accident Review
A notable exception is West Midlands Police who publish
2
angel road
software an annual Accident Review West Midlands figures for excessive speed accidents are as follows non-pedestrian causes pedestrian causes excessive speed fatals serious overall fatals serious overall 1999 930% 625% 046% 294% 072% 046%
TRL 323 was an in-depth investigation by the Transport Research laboratory into a New system
2
angel road
software for recording contributory factors in road accidents It involved 8 UK Police forces on a trial basis One test of effectiveness was to be Would the 8 forces yield similar results Similar results
2
angel road
software were obtained indicating that the system was operated correctly and consistently There`s much talk about TRL323 and we`re planning a detailed page discussing the report We have a copy which we are not
2
angel road
software allowed to post for download and it`s very clear indeed to us that the report is good and clear that the system was defined properly and worked correctly that skilled police officers made
2
angel road
software valid and valuable judgements about each accident that consistency across the 8 regions means that the results were true and unambiguous excessive speed number of factors percentage of factors against 2795 total accident
2
angel road
software reports
these percentages are not calculated or included in the report definite factors 126 60% 45% all factors 424 73% 152% TRL323 allowed factors to be classified as definite probable and possible
2
angel road
software Where the table above lists all factors that includes excessive speed as a definite probable and possible factor It follows then that the all factors figures include cases where the excessive speed was
2
angel road
software only a possible factor These TRL323 factors are contributory factors not causation factors In fact TRL323 recognises that most accidents have complex causation and cleverly avoided the pitfall of trying to make reporting
2
angel road
software police officers identify the primary causation factor from a number of contributory factors This approach gives freedom for the reporting police officers to record observable details without have to make fine value judgements
2
angel road
software about which factor actually caused the accident TRL323 general methods are widely respected as the best way to gather contributory factor information
except perhaps by those who have an agenda Which brings
2
angel road
software us to the last column in the table above The calculated percentages shown in the last column do not appear anywhere in TRL323 but latterly those with an agenda have suggested that the
2
angel road
software true excessive speed value from TRL323 should have been 152% based on a calculation that the impartial authors considered unnecessary If anyone quotes the 152% figure from TRL323 you will know to point
2
angel road
software out that it includes possible and probable excessive speed accidents as well as definite ones new We would like to present the split in TRL 323 between possible probable and definite factors in
2
angel road
software the excessive speed catagory new table excessive speed factors TRL323 number of times recorded percentage of excessive speed factors percentage of 2795 accident reports possible 68 16% 24% probable 163 38% 58% definite
2
angel road
software 126 30% 45% confidence not reported 67 16% 24% all 424 100% 152% We might make some guesses about how many of those factors represent a genuine excessive speed accident We suggest a
2
angel road
software reasonable guess could be based on 30% of the possible factors 20 75% of the probable factors 75% of the confidence not reported factors 50 100% of the definite factors 318 318 factors
2
angel road
software from 2795 reports suggests a new percentage of excessive speed accidents of 113% We`re still a very long way indeed from one third DfT The DfT have accident causation data which they are
2
angel road
software not publishing We have written to request information but had no reply This document contains Fifteen police forces are currently supplying contributory factor information to DfT using the proposed national form on a
2
angel road
software voluntary basis We need that data It`s of enormous public interest The DfT committee is called Standing Committee on Road Accident Statistics SCRAS The former senior person Peter Wilding still mentioned in the
2
angel road
software documents has left The senior person now is Alan Oliver If you feel like chasing this up please do so Finally some of this data has been published on the 30th March 2005
2
angel road
software It is contained in a report called review of the contributory factors system and can be downloaded from the DfT This is by far the largest published survey of accident causation data in
2
angel road
software the UK in recent decades and the data was compiled with the excellent TRL323 system The conclusion is that excessive speed was coded as possible probable or definite for 7600 out of 60797
2
angel road
software accidents That`s 125% which is no where near one third As usual this catagory includes inappropriate speed within the speed limit see below The top 7 contributory factors as reported were Inattention 258%
2
angel road
software Failure to judge other person`s path or speed 226% Looked but did not see 197% Behaviour careless/thoughtless/reckless 184% Failed to look 163% Lack of judgement of own path 137% Excessive speed 125%
