From Petrolhead Porkies by
Cowboy Cops to Elephantine Eighteens via Bayesian Bananas
Independent 15jun04 News
Death rate 'down at speed camera sites' The
Government hit back at … critics today by publishing figures ... Produced by
University College London … showed deaths and serious injuries had fallen by an
average of 40 per cent…. equivalent of 100 fewer deaths a year - a figure
hailed by Transport Secretary Alistair Darling, and safety and environment
groups. But …Safe Speed …said the figures were "deeply flawed"
…Association of British Drivers said …far lower than that of some European
countries. …42 police force areas …are now in … money raised goes into camera
activity and the Treasury receives any surplus... 870 fewer KSIs per year…33 per cent fall in injury accidents -
4,030 fewer per year …a 35 per cent reduction in … pedestrians killed or
seriously injured. Average speeds … fell by 7 per cent 2.4mph …at urban sites …
around 8 per cent …vehicles speeding at
new camera sites dropped by 71 per cent …79 per cent of people surveyed
supported … benefit … through casualties saved … £221 million a year Mr Darling
…recognised …controversy … people felt resentful …figures prove that cameras
save lives. …"Up to 10 people are killed on our roads each day. We owe it
to them and their families to do everything we can to improve road safety even
further. "Most …sites …achieved good results. …where results were not as
good …see what more could be done ..." …published the location of every
site …show why …installed and …effect
…ensure …are needed ..."
Conservatives said …suspicion …to raise money… Liberal Democrats said
…would silence …advocated the removal …Association of Chief Police Officers
said …cameras did …save lives AA Motoring Trust said …cameras were about safety
and not revenue. Paul Smith… Safe Speed Safety Campaign, said …were flawed.
Independent 16jun04 News
Drivers dismiss speed camera safety claims A
furious dispute … Association of British Drivers (ABD) said …
"meaningless" …no substantial reduction in accidents …government
adviser warned sceptics …"blood on their hands" … University College
London, published by the Government, showed people killed or seriously injured
…fell by 40 per cent over three years to mid-2003 …benefit to society of £221m
a year. ...reduction in …collisions involving injury varied from 11 per cent
…to 72 per cent … Mark McArthur-Christie ABD, … no …decrease in accidents since
…installed…."cluster" …at one site in one year… at another site the
next year. David Begg, chairman
Commission Integrated Transport, a government advisory body, …:"Today's
report proves that speed kills, that cameras reduce speeds at accident spots
and they prevent injuries and save lives." Critics of speed cameras would
"end up with blood on their hands". Department for Transport said
casualties had risen at 743 out of the 5,000 sites… spokesman said …not been in
place long enough to judge….
Independent 21jun Letters
Speed cameras should be controlled by
independent traffic police: Sir:
…official report concluded speed cameras save lives …virtually all in the right
place should come as no great surprise. The Government likes cameras. I am
surprised that … effort and fanfare … only saving 100 lives a year. …I view it
as a poor return on the investment. …not assessed how many accidents speed
cameras cause….having to concentrate more on speed and less on driving is
dangerous and causes fatigue, a major cause of accidents. …greater emphasis on cameras
and reduction of traffic police …more drink drivers, more dangerous vehicles
and other serious offences going undetected. How many lives has this cost?
Without considering these issues the report is meaningless. …a powerful lobby
determined to increase the number of cameras no matter what. A balanced and
sensible debate seems unlikely. …an independent national traffic police force
…control of the cameras … unaccountable "safety partnerships" would
aid public confidence. This would allow ….money from cameras to fund additional
officers and education…. some confidence …used sensibly …not just as cash cows.
…halt the real damage which is being done between the police and the public.
SWERVILITY SIMPLISTICILITY SUGGESTIBILITY SUSPECTIBILITY
SPINILITY
REPORT The sites
that were accepted for inclusion in the cost recovery programme conformed to
the handbook requirements that are specified in Appendix A of the present
research report. The requirement for a record of PICs during recent years is a
central criterion for selection. However, there was also a requirement to
identify speed as a contributory factor to these collisions, a clear indication
of motorists speeding, suitability of the site for treatment by enforcement,
and unsuitability of further engineering remedial measures. Because of this
requirement to identify the sites as suitable for this particular safety
measure, and in particular that the collision record was not the sole criterion
for selection, the established statistical phenomenon of regression to the mean
(also known as bias by selection) will not apply in full measure. Furthermore,
the results of the statistical analysis of casualties and collisions at speed
cameras are consistent with the observed reductions in speeding, showing that
the enforcement measures are working as intended.| We cannot, in all cases,
make comparisons with the results from the previous report as there have been
refinements in the modelling techniques used and an increase in data. Where
there have been substantial changes to the results found last time, these are
highlighted and, where possible, explained. | modelling gobbledegook p93-5
MELDREW In round terms say 3kpa
deaths, 30kpa injuries, 300kpa incidents, 3000kpa speeders (projected),
30000kpa drivers corresponding to equivalent intervals of 10y/speeder,
100y/incident, 1000y/injury, 10000y/death. Current fines £60Mpa from 1M
speeders of which 60%+ is spent on supply-support. As simple suggestion suppose
3600 deaths site-risk partitioned as 1800 high, 1200 medium, 600 low and
suppose high and medium are cameraed but not low ~ perhaps plausibly associate
each category with 1000 sites so high equates to 2- deaths, medium to 1+ and
low to 1- (yearly). These segmented flat distributions could then be seen as
segmented mean values of a linear profile over all events ranging down from
2100 to 300, with high band 2100-1500, medium band 1500-900, low band 900-300
and divide by 1000 for incidence per site.
Doing this we
could then recover the 100 camera attributed reduction plausibly by shifting
the high-medium scale from 2100-900 to 2050-850 such that the supposed uniform
50 reduction divided by 1000 for incidence times 2000 sites returns the
observed 100 reduction. However a subsidiary observation was increased
incidence at 1/6th or so of cameraed sites. Some maybe all of this
increase reflects annual variability but if we want to assign it all within the
simple representation then one of two simple limit attributions would be to put
it all in medium range and suppose for example that the high mean had shifted
down by 200 from 1800 to 1600 and the medium mean had shifted up by 100 from
1200 to 1300. Segmented linear distributions would then run from 1900-1300 for
high set and 1600-1000 for the medium set such that a single linear fit running
down from 1900 to 1000 would have mean value 1450 against 1500 before and so
this 50 reduction divided by 1000 times 2000 sites again recovers 100 fewer
deaths. This linear profile (1900-1000) would then cross the original one
(2100-900) at 1300 on the death rate corresponding to 2/3 sites having a
reduced rate and 1/3 having an increased rate.
You can see how
this might be easily tuned to return the 1/6th or so recorded but
it’s just not worthwhile given uncertain variability. However commonsense
suggests that if medium risk sites returned a higher than expected rate then
this behaviour quite probably wasn’t special but spilled over into the low risk
range originally suggested as 900-300 (mean 600). Indeed, not just commonsense
but also nigh on steady state overall records ~ meaning that if the net 100
reduction obtained over all cameraed sites was attributed entirely to
variability (not causative consequence) then an increase of 100 deaths would
have occurred at uncameraed ones taking their mean up to 700 which here would
be simplistically assigned a linear profile 1000-400. If the case for
installing more cameras could only be made on grounds of death rate exceeding a
threshold then 1pa would threshold opening this door to the top end of the
uncameraed ones.
By the same
token even with all of the 1/6th “mysteriously increased” sites
dumped into the medium bin some at least likely deserve decamering being
borderline to the same threshold ~ “mysterious” that is to Ali Darling in his
Toady spot though not to grumpy old gits like me traditionally trained in
turbulence! In fairness, Ali did indicate that some cameras would be pulled
although also stated that total numbers would be increased in view of their
successful demonstration ~ and that’s cheating because you really can’t claim
causation on one side of the fence but merely mystery on the other.
As another
indicator of the fallaciously claimed causation consider that deaths broadly
carry companion ratios of injury, perhaps 6:1 for major each with 6:1 for
minor, in all then 36 injuries for each death, these figures as overall numbers
for all events from fatal accidents to minor bumps. This ratio was reproduced
in the summary claims (deaths down by 100, injuries by 4000) when it really
shouldn’t have been because the camera assignment was biased toward the most
dangerous sites as dictated by approval regulations. It’s not clear which way
injury numbers should have gone because some death reduction must have been
converted into injury amplification whilst some presumably had no associated
conversion.
But observed
ratio conservation accompanied by claimed camera causation seems an implausible
pairing without any assay that details the trade-off between push and pull
(none was delivered). Indeed, the two going together arguably points to prima
facie indication that the data were dominated by variability alone! And that’s the rub here as indeed with most
mantras of the “speed kills” variety ~ statistical massaging can always provide
what the politicos want whether or not it connects with commonsense.
Apologetically adapting Einstein and Rutherford adages into the twinned tag
“God didn’t dice Man merely to play pinhead fairies with elephantine eights on
Bayesian Bananas” is about the neatest way of summing up this dicing of data
into an elephantine eighteen whose complexity means it can’t be constructively
deconstructed even for plausibility never mind sensitivity or reproducibility.
Nonetheless I
had a crack at accounting for the 1/6th sites supposedly where cameras
had caused increased incidence of casualties ~ yes, caused because you can’t
claim causative connection on your side of the fence without conceding it on the
other. This will appear very soon as postscript suggesting what was claimed to
be a conundrum may well be instead an embarrassing explanation of statistical trickery
played to provide promotional purpose for what in reality was always a political
policy, one that has always been motivated and maintained by no more than a
mantra pandering to familial grief of unfortunate victims not so much of speed
killers but of senseless stupidities ~ some as extreme excesses but mostly by
far almost certainly inane inattention or insensitivity to impact consequences comparable
.with those conveyed in carrying of a lethal weaponry.
My meldrewism portrays
Peter & Jane’s rendering of the same story as one that allows Humpty-Dumpty
to be both cracked open and patched up again. Inspired as the simplified
picture posed above it provides a parametric portrait that is probably about as
much as Einstein and Rutherford would have tolerated given all the variability
and uncertainty in capturing and collating such data. It is of course
self-evident that realities of different driving behaviours broadly reflect sensitivities
on a spectrum from disdain to discomfort, this scaling in turn broadly aligned
with actuarial actualities of age dependence for accident incidence. The most
meaningful generic metric of course is frequency spectrum of g-force but that’s
rather fancy not to say fanciful for general guidelines digestible by other
than sensibly schooled scientists. A crude cartoon can be conveyed in terms of g-bands
ranging downwards from excitingly accessible to grudgingly tolerable, dominantly
discriminated within a triad of decadal age aggregates respectively from young follies
(20-40) adrenalising on 4/3g twitching tricks through middling fifties (40-60) fearful
of 2/3g abrupt encounters to old farties (60-80) discomforted by 1/3g neck benders.
These things are the decisive
discriminators that not only set speeds seen as standard away from camera cavorting
but also provided practical policies for policing in earlier eras before focus
follies eliminated this established equilibrium. As seen below the numbers are pretty
much on the button as indicators for speeds seen as endemic excesses, upwards
from 20% for the farties through 30% for fifties to 40% for the follies ~ respectively
36, 39, 42 in 30- zones and pro rata
for 60- and 70- zones, all in line with established experience for drivers and policers
as realities that have stupidly been sidelined by partnerships poseurs pontificating
from their privileged hi-profiled platforms.
Anyway I did this simple stuff within
a week of that ridiculous report and it would have appeared at the time had I
not been distracted by disrupted email courtesy of antispam silliness adding to
already seriously depleted accessibility courtesy of a virus mailer impersonating
my URL (woes to be related in a future meldrewism). Amusingly ironic then that
during the delay Ali D has judged multi-million alienation of respectable law
abiders would be too much to Blair in the upcoming general election and acted
to reduce the penalties that were threatening the livelihoods of not just many
movers but many makers who wouldn’t sit idly by, indeed were already banging
their angry drums well within hearing range of Westminster’s Woolly Wilderness.
By extraordinary coincidence Ali’s new
brainwave is bulls-eyed on my own portrayal (bang-on at 30% = 39!)~ well, well
actuarial actualities finally found their place in policies that previously had
been pirated by partnership pontificateurs whose leading lights number that
obnoxiously opinionated ACPO pop-idle with the funny Scandinavian-sounding name
~ the man whose main claim to fame has been having not just the most cameras per mile with the most stringent settings but
also the most ruthless readiness to prosecute the hapless Henries who happened
to ruffles his sensitivities on his patch, a biggish regional outback and no
doubt a happy hunting ground during the summer season. You don’t have to take my
word ~ replay his Toady spot 26Jun04 (BBC R4 website ~ google it!) and judge
for yourself whether you’re listening to an obsessive carer or merely a maker moving
up his poky political pole!
This is where I sign off for now having
finally finished it 3 months later than planned ~ prettification is a
gargantuan gorger of time and time used to be so precious a commodity that prettification
was seldom seen outside sales and advertising arenas. Nowadays of course with
so much of slender substance, prettification has displaced pontification as
primary point of promotion, mostly of course pointless pap with such shortened shelf-life
as to provide a presumed primary purpose to the repetitive renderings of anything
and everything however flawed or fatuous.
PA-C’s pro camera
interest predisposed prejudice (at best covert with micro-c) in their
pejorative portrait, a betrayal which triggered my googling for evidence of
conjectured conflict to retrieve a trio of top tenners as prima facie pointers,
suspicions endorsed also by absolute absence of anything via their own site
searched for “speed cameras” when I expected to see site screamers for
successful selection in a panful of pro projects procured from present partial
politicos. DoT seriously contaminated credibility in their Sec State trumpeting
of the report as a product of UCL impartial excellence, especially as no
attention (nor mention even) was drawn to PA participation ~ extraordinary
considering the glossy navel-glazer itself was topped and tailed with PA
adverts for their incomparable arena acumen. Integrity wasn’t merely evaporated
by this bunch of bungling bandits as ambushed and extinguished in alliance with
ambitious adventurers and avaricious academics. Poor old GB ~ yet another
splash down the Suwannee and not even a paddle in sight to possibly prevent
impaling on the debris of our dilapidated Dome and all the other doomed dogmas
that Downing Street has spewed since they stole the showboat from a comparably
crackpot crew.