Safe Speed Forums

The campaign for genuine road safety
It is currently Sun Jun 14, 2026 17:05

All times are UTC [ DST ]




Post new topic Reply to topic  [ 9 posts ] 
Author Message
PostPosted: Tue Mar 22, 2005 03:40 
Offline
Site Admin
User avatar

Joined: Sat Mar 06, 2004 06:46
Posts: 16903
Location: Safe Speed
Papers published by the Royal Statistical Society include an estimate for Speed Camera RTTM of 18% on KSI collisions from forthcoming research.

See: http://www.rss.org.uk/rssadmin/uploads/ ... 0nov04.pdf Page 21.

This shows RTTM for fatal and serious crashes of -18%, with 95% confidence limits of -25%, -9%. (i.e. the true value lies in the range -9 to -25%).

Net benefit of the camera is calculated as -6% and 95% confidence limits are: -21%, +12%. Yes, that's right folks, it's entirely possible that crashes even at camera sites went up as a result of the camera.

Worryingly, there's also a traffic flow difference of -5%, and this would normally indicate that 1 in 20 vehicles diverted to a less safe road because of the camera.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety


Top
 Profile Send private message  
 
 Post subject:
PostPosted: Tue Mar 22, 2005 10:30 
Offline
Member
Member

Joined: Thu Mar 11, 2004 00:24
Posts: 2400
Location: Kendal, Cumbria
So if we can presume that a 5% reduction in traffic will give a 5% reduction in accidents, is it reasonable to say that then the net benefit is actually -1% ? Is this a reasonable assumption, or is there a better statistical correlation available between traffic levels and accident incidence, all other things being equal.

Either way, this would seem to indicate that cameras make pretty much no measurable difference whatsoever, as the value is so small (whether positive or negative) as to be all but swamped by RTTM.

_________________
CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!


Top
 Profile Send private message  
 
 Post subject:
PostPosted: Tue Mar 22, 2005 12:10 
Offline
Banned
Banned

Joined: Thu Apr 15, 2004 12:47
Posts: 2291
JT wrote:
So if we can presume that a 5% reduction in traffic will give a 5% reduction in accidents, is it reasonable to say that then the net benefit is actually -1% ? Is this a reasonable assumption,


No - I suspect that would be subtracting the benefit due to 'change in flow' twice. This particular table demonstrates only the reduction in total accidents. It does not indicate in any way the benefit due to reduced severity (due to lower average speeds) of those accidents that do occur.

_________________
I stole this .sig


Top
 Profile  
 
 Post subject:
PostPosted: Tue Mar 22, 2005 12:24 
Offline
Site Admin
User avatar

Joined: Sat Mar 06, 2004 06:46
Posts: 16903
Location: Safe Speed
basingwerk wrote:
JT wrote:
So if we can presume that a 5% reduction in traffic will give a 5% reduction in accidents, is it reasonable to say that then the net benefit is actually -1% ? Is this a reasonable assumption,


No - I suspect that would be subtracting the benefit due to 'change in flow' twice. This particular table demonstrates only the reduction in total accidents. It does not indicate in any way the benefit due to reduced severity (due to lower average speeds) of those accidents that do occur.


Actually there's a stong indication of an increase in crash severity. The claim is that injury crashes are significantly reduced while 'ksi' crashes are reduced insignificantly. That's clearly an increase in average crash severity.

When are these people going to wake up?

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety


Top
 Profile Send private message  
 
 Post subject:
PostPosted: Tue Mar 22, 2005 12:30 
Offline
Site Admin
User avatar

Joined: Sat Mar 06, 2004 06:46
Posts: 16903
Location: Safe Speed
Here's a view based on Linda mountain's findings:

DfT say crashes down at camera sites by 40% leading to 100 lives per year saved by 5,000 cameras.

Linda says, no, it's only 6%.

6/40 * 100 = 15 lives saved.

5000/15 = 1 life saved per 333 camera years.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety


Top
 Profile Send private message  
 
 Post subject: Road improvements
PostPosted: Tue Mar 22, 2005 12:46 
Offline
Life Member
Life Member

Joined: Wed Dec 01, 2004 20:14
Posts: 252
Location: Hampshire
Very interesting analysis which can be quoted as only a 6% reduction in FSA (fatal & Serious?)

We know that some camera sites have also had road improvements.

I did not notice that mentioned in the analysis.


Top
 Profile Send private message  
 
 Post subject:
PostPosted: Tue Mar 22, 2005 13:41 
Offline
Life Member
Life Member

Joined: Sat Mar 27, 2004 13:50
Posts: 2643
basingwerk wrote:
It does not indicate in any way the benefit due to reduced severity (due to lower average speeds) of those accidents that do occur.


The link between average speeds and accident severity exists only in your imagination.
It would only hold true in a world where everybody drove around with eyes glued to their speedos and not paying the slightest attention to the road ahead. And the number of casualties would probably be two or three orders of magnitude higher than they are.
But as most drivers, most of the time, watch the road and adjust their driving according to hazards, that link doesn't exist in real-life.

Cheers
Peter


Top
 Profile Send private message  
 
 Post subject:
PostPosted: Tue Mar 22, 2005 21:56 
Offline
Friend of Safe Speed
Friend of Safe Speed
User avatar

Joined: Thu Mar 11, 2004 11:19
Posts: 1795
You don't have to have your eyes glued to the speedo to be affected by the speed kills policy though. I find I spend more time thinking about whether I am within the speed limit then I did before. Frankly it is a wasted thought as I should be thinking about the road ahead and what is going on around me rather than whether my speed matches that on the lollipops. I also find I am tending to drift along at whatever speed is on the signs rather than actually thinking about appropriate speed like one does in nsl limits.

Conversely I did go through a village where the residents had written a load of signs saying 'slow down' speed kills yada yada and I wondered how long it is before one of them gets run over as a driver was too busy reading their hand written signs :twisted:


Top
 Profile Send private message  
 
 Post subject:
PostPosted: Tue Mar 22, 2005 22:45 
Offline
Site Admin
User avatar

Joined: Sat Mar 06, 2004 06:46
Posts: 16903
Location: Safe Speed
teabelly wrote:
You don't have to have your eyes glued to the speedo to be affected by the speed kills policy though. I find I spend more time thinking about whether I am within the speed limit then I did before. Frankly it is a wasted thought as I should be thinking about the road ahead and what is going on around me rather than whether my speed matches that on the lollipops. I also find I am tending to drift along at whatever speed is on the signs rather than actually thinking about appropriate speed like one does in nsl limits.


:yesyes: Oh yes. It's massive. The effects are absolutely everywhere.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety


Top
 Profile Send private message  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 9 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You can post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group
[ Time : 0.092s | 11 Queries | GZIP : Off ]