Safe Speed Forums

ROSPA CARE ON THE ROAD MAGAZINE, OCTOBER 2006

CAMERA SUCCESS

The number of people hurt or killed on Plymouth roads has dropped dramatically after speed cameras were fitted. The total number of
incidents before 2002 was 124 compared with 41 in 2006, according to Devon and Cornwall Safety Camera Partnership's latest figures.

It says the figures show that the 34 cameras do work. A spokesman said, "The myth is that cameras are there to catch motorists out and raise revenue. But the purpose is to change driver behaviour."


Light the blue touchpaper & retire.....

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Anyone who tells you that nothing is impossible has never bathed in a saucer of water.

I think the Devon and Cornwall partnership have been praising the plymouth cameras for a while. Usual stuff really. Notice how, like everywhere else, that the cameras are mostly on main roads (from checking camera sites on www.speedcameramap.co.uk).

FWIW, I suspect that the real reason why KSI has dropped in Plymouth (if it has) is because of the amount of congestion caused by redevelopment of Drake Circus, around Derriford, etc. Basically, nobody can go fast enough to cause injury!

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Will

I'm amazed that these cameras have managed to prevent people KSIed at low speeds below the limit, typically as a result of drivers not concentrating on the road, dangerously overtaking vehicles, even those indicating right, as well as reducing incidents involving numpty pedestrians.

Clearly the vast bulk of the claimed 'benefit' is in fact RTTM.

Or to put it another way, I DO NOT believe that they don't know better.

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

Paul, you're jumping to conclusions. RTTM requires the same road system before and after, which is what Plymouth doesn't have due to extensive redevelopment work. For example, they've converted one accident-prone roundabout to a light-controlled junction and in doing so altered the traffic flow patterns for about two thirds of the city centre. To the North, they've completely re-engineered the roads around Plymouth Airport, which contained two accident blackspots, and removed the "pinch" in the northbound approach to Southway Drive.

IMO, the benefit is likely to be real but very much more likely due to engineering improvements than speed cameras!

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Will

http://news.bbc.co.uk/1/hi/england/devon/5356184.stm

What exactly does "before 2002" mean? Just 2001 or the sum total from 1800 to 2001?

I am certainly not 'jumping to conclusions'. The design of the speed camera programme leads to a selection bias which leads to a RTTM benefit illusion at speed camera sites. The BBC report confirms that the claimed benefit is 'at speed camera sites'. I have taken camera partnership claims apart hundreds of times, and EVERY SINGLE CLAIM (of this nature depends on RTTM. This one is no different.

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

So then, you would attribute the difference between KSI on one particular road in one year and its newly-opened bypass in the next to RTTM?

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Will

Yawn. The claim is 'at camera sites'. If you don't map it one to one {camera site 2001; camera site 2006} you get an increase in crashes due to the increase in the number of camera sites.

So YES. It's largely RTTM.

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

That's what I was thinking. If it is just 2001, it's certainly unnecessarily clumsy wording.

Is it? I know that's usually the case with these claims but in this case I dont see any mention of such specific sites (unless you know something I don't?)

<fe>Yawn. Oh no it isn't!</fe>
The before and after figures relate to effectively different roads. For example, consider Royal Parade:

Changes: The three lanes each side were converted from one bus lane and two general use lanes to two bus lanes and one general use lane. Pedestrian underpass has been replaced by light-controlled crossings with speed humps. Speed cameras erected both directions.

Effects: Traffic volume reduced because the main through route has effectively moved from Royal Parade to Cobourg Street (where there are no speed cameras). Traffic arriving at the roundabouts at each end of Royal Parade is now single file, which has all but removed the "two lanes into one" potential conflict at the exits to those roundabouts. Traffic has been reduced to a crawl because of the increased density from removal of one GP lane and even when free-flowing is restricted by the speed bumps.

Conclusion: Any reduction in casualty figures for Royal Parade and the roundabouts at either end are probably due to changes in layout and not speed cameras.

It's the same for many parts of the city. Plymouth has undergone radical redevelopment in the last couple of years and coincident with engineering treatments, the pratnership has set up cameras. So although the names of the locations at which these cameras are erected has remained the same, the roads have changed and are radically different. Comparing figures before and after the cameras is thus like comparing chalk and cheese. The engineering works meant that the roads carried less traffic as motorists take alternative routes to avoid the congestion and those works have removed many potential causes of collisions (e.g. the "two into one" problems that existed either end of Royal Parade), making those roads intrinsically safer.

The roads have changed so much that the old mean is meaningless in the new system, and so any claim of regression to that old mean cannot be valid. However, for the same reasons, any attributing of casualty reduction to speed cameras is likewise invalid.

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Will

Perhaps it isn't in the newspapers, but it is on the pratnership's own site:
http://www.devon-cornwall.police.uk/dcs ... 210906.htm

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Will

Has everyone taken stupid pills this morning or something?

Mate, read the BBC link you posted yourself.

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

oh sh*t, yeah!
I didn't spot the forest for the trees (and if we're foing to be honest it was quite a big forest), I went straight for the body text. I can't believe I fell for that - time to stop taking those tablets

Devon & Cornwall didn't exactly have a good record until 2002, and they hadn't reduced Killed in comparison to 1995. These where the K-KSI's upto 2004, don't have them for 2005. The partnership was Launched on 18th October 2002.

Devon....................................Cornwall

Year.........K............SI..............Year.............K..........SI

1995........41..........657...........1995............38........325
1996........57..........672...........1996............40........343
1997........56..........633...........1997............45........308
1998........53..........545...........1998............37........311
1999........48..........502...........1999............30........272
2000........59..........506...........2000............35........291
2001........53..........503...........2001............40........295
2002........56..........512...........2002............53........280
2003........45..........450...........2003............30........306
2004........42..........336...........2004............44........224

I'm also not sure what they meant by "incidents" in the BBC article. Do they mean SI's.

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Useless laws weaken necessary laws.

I've just plotted it and...........no drop in K over the period.

Well done D&C!

So if you add 2004 K SI for Devon........ 42 + 336 = 378 Total KSI = 646
..........................................Cornwall..... 44 + 224 = 268

2005 figures. They don't split K SI it's all KSI

Devon........410 KSI Total KSI = 671
Cornwall....261 KSI

Total KSI 2004 = 646
Total KSI 2005 = 671

If I'm right, as a total they're still up.

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Useless laws weaken necessary laws.

We know (from the pratnership's own claims) that KSI for Plymouth has gone down, and the overall values are the same. Thus, we can deduce that the remainder of Devon must have had a large increase. Now, from my observations, the engineering improvements are the most likely cause of the reduction in Plymouth.

So, the reductions in KSI are attributable to something other than speed cameras, and areas where the only treatment is speed cameras have seen increases in KSI.

Ergo speed cameras don't work.

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Will