Speed Cameras, are they for safety, or revenue?

[Devil2575]

Phatboy317 said:

You said my assessment of the risk is based on theory, so I assumed you accepted the theoretical basis.
But if you need it explaining then I'll try to accommodate you - but not before tomorrow evening - I'm off to bed now and I have a very busy work schedule tomorrow,

Yes I know I said theory but I wasn't talking about a model. You'd need to produce a model based on the theory first.

Phatboy317 said:

No. That example was to lend some perspective to your point about other roads users not expecting you to be travelling faster than a certain speed - it has nothing to do with the relative risk factors.

But it was just a made up scenario and i'm not sure what perspective it was supposed to lend. The concept of another driver not expecting you to be travelling in excess of the speed limit is farily straight forward. You created a complicated hypothetical situation to try and counter this but I don't think it adds anything at all.

It still doesn't change the fact that the relative risks comes from data.

I don't have an issue with the data. They could have used more data but given how it was collected I can understand why this was a limitation on the study.

[MGJohn]

Devil2575 said:

The probability of getting heads when I toss a coin is 0.5. But that doesn't tell me the result of a coin toss and in fact it's perfectly possible to get a run of 10 tails. What it does tell me is that with a large number of coin tosses you will get 50% heads.

What if it lands on its edge? .... 'appens...

[Devil2575]

MGJohn said:

Devil2575 said:

The probability of getting heads when I toss a coin is 0.5. But that doesn't tell me the result of a coin toss and in fact it's perfectly possible to get a run of 10 tails. What it does tell me is that with a large number of coin tosses you will get 50% heads.

What if it lands on its edge? .... 'appens...

I'm going to guess that it does so so infrequently as to be statistically insignificant

[singlecoil]

Devil2575 said:

MGJohn said:

Devil2575 said:

The probability of getting heads when I toss a coin is 0.5. But that doesn't tell me the result of a coin toss and in fact it's perfectly possible to get a run of 10 tails. What it does tell me is that with a large number of coin tosses you will get 50% heads.

What if it lands on its edge? .... 'appens...

I'm going to guess that it does so so infrequently as to be statistically insignificant

My guess is that it happens more often than situations where driving faster is actually safer than driving slower.

[Phatboy317]

Devil2575 said:

Phatboy317 said:

You said my assessment of the risk is based on theory, so I assumed you accepted the theoretical basis.
But if you need it explaining then I'll try to accommodate you - but not before tomorrow evening - I'm off to bed now and I have a very busy work schedule tomorrow,

Yes I know I said theory but I wasn't talking about a model. You'd need to produce a model based on the theory first.

Phatboy317 said:

No. That example was to lend some perspective to your point about other roads users not expecting you to be travelling faster than a certain speed - it has nothing to do with the relative risk factors.

But it was just a made up scenario and i'm not sure what perspective it was supposed to lend. The concept of another driver not expecting you to be travelling in excess of the speed limit is farily straight forward. You created a complicated hypothetical situation to try and counter this but I don't think it adds anything at all.

It still doesn't change the fact that the relative risks comes from data.

I don't have an issue with the data. They could have used more data but given how it was collected I can understand why this was a limitation on the study.

Ok, here's the model, all bog-standard physics:

Stopping distance is determined as:

D = (R * S) + (S * S / (2 * f * g))

where: D = stopping distance (metres), R = reaction time, S = speed (metres/sec), f = friction coefficient and g = gravitational constant (9.81)

And the probability of being between two points at any point in time is proportional to:

d / S

where d = the distance between the two points

So, substituting D for d, the probability of a car being within its stopping distance of an object at the moment the object appears in the road ahead, is proportional to:

((R * S) + (S * S / (2 * f * g))) / S

which is simplified to:

R + (S / (2 * f * g))

Assuming a reaction time of 0.7 seconds and a friction coefficient of 0.8, this predicts a 5% increase in probability of a collision at 65km/h over 60km/h

To my mind, the notion that this 5% is magnified to 100% simply because of something like other road users expecting your speed to be 5km/h lower, requires quite a large leap of faith.
There may be such mechanisms, but until they have been identified, studied, well-understood and quantified, I remain deeply sceptical.

[Devil2575]

Phatboy317 said:

Ok, here's the model, all bog-standard physics:

Stopping distance is determined as:

D = (R * S) + (S * S / (2 * f * g))

where: D = stopping distance (metres), R = reaction time, S = speed (metres/sec), f = friction coefficient and g = gravitational constant (9.81)

And the probability of being between two points at any point in time is proportional to:

d / S

where d = the distance between the two points

So, substituting D for d, the probability of a car being within its stopping distance of an object at the moment the object appears in the road ahead, is proportional to:

((R * S) + (S * S / (2 * f * g))) / S

which is simplified to:

R + (S / (2 * f * g))

Assuming a reaction time of 0.7 seconds and a friction coefficient of 0.8, this predicts a 5% increase in probability of a collision at 65km/h over 60km/h

To my mind, the notion that this 5% is magnified to 100% simply because of something like other road users expecting your speed to be 5km/h lower, requires quite a large leap of faith.
There may be such mechanisms, but until they have been identified, studied, well-understood and quantified, I remain deeply sceptical.

But this is based on the theoretical concept of an object randomly appearing in the road. Aside from perhaps animals that may simply run out at any time it doesn't really represent the majority of real life situations.

[Phatboy317]

Devil2575 said:

But this is based on the theoretical concept of an object randomly appearing in the road. Aside from perhaps animals that may simply run out at any time it doesn't really represent the majority of real life situations.

Well, once those real-life situations are identified and the mechanisms understood and quantified, instead of just being tilted at, I'm prepared to listen.

[woof]

Speed cameras ‘increase risk of serious car crashes’ in some areas, RAC claims
http://metro.co.uk/2013/06/07/speed-cameras-increa...

[vonhosen]

woof said:

Speed cameras ‘increase risk of serious car crashes’ in some areas, RAC claims
http://metro.co.uk/2013/06/07/speed-cameras-increa...

Why did they select only those 551 sites & why has the risk only increased at 21 of those 551 sites?

[singlecoil]

vonhosen said:

woof said:

Speed cameras ‘increase risk of serious car crashes’ in some areas, RAC claims
http://metro.co.uk/2013/06/07/speed-cameras-increa...

Why did they select only those 551 sites & why has the risk only increased at 21 of those 551 sites?

My guess is that the cameras were incorrectly mounted and kept falling into the road, that's the only way they could cause accidents.

[Devil2575]

vonhosen said:

woof said:

Speed cameras ‘increase risk of serious car crashes’ in some areas, RAC claims
http://metro.co.uk/2013/06/07/speed-cameras-increa...

Why did they select only those 551 sites & why has the risk only increased at 21 of those 551 sites?

This is an interesting take on a report done by the RAC and show a good example of a news paper reporting a story in a certain way.

The original RAC report is here:

http://www.racfoundation.org/research/safety/effec...

and the update is here:

http://www.racfoundation.org/research/safety/speed...

What Metro has done is take a part of the report and highlight that as the main news story. They haven't even got the mans name right which doesn't bode well for the standard of reporting.

I'd need to look at the detail of the report to be honest. It could indeed highlight a problem with 21 out of the 551 sites, but given the random nature of accidents i'd be interested to know how many additional crashes took place at these sites to account for the increase.

The overall view of the report though is that on average fatalites and serious collisions fell by 22% at the 551 sites looked at.

[Jasandjules]

Devil2575 said:

It could indeed highlight a problem with 21 out of the 551 sites, but given the random nature of accidents i'd be interested to know how many additional crashes took place at these sites to account for the increase.

The overall view of the report though is that on average fatalites and serious collisions fell by 22% at the 551 sites looked at.

Random nature? Surely you mean "caused by exceeding the speed limit"?

Fatalities are falling on the roads due to vehicular safety improvements. Not because of the Scameras.

[Phatboy317]

vonhosen said:

woof said:

Speed cameras ‘increase risk of serious car crashes’ in some areas, RAC claims
http://metro.co.uk/2013/06/07/speed-cameras-increa...

Why did they select only those 551 sites & why has the risk only increased at 21 of those 551 sites?

Here's the full report

Edit: it seems the Devil pipped me to the post

Edited by Phatboy317 on Thursday 29th January 17:56

[Devil2575]

Jasandjules said:

Random nature? Surely you mean "caused by exceeding the speed limit"?

Fatalities are falling on the roads due to vehicular safety improvements. Not because of the Scameras.

No, accidents are to a large degree random because they rely on number of unrelated factors coming together. Certain factors increase the risk of having an accident or the severity of it but that doesn't guarantee that one will occur.

[woof]

Devil2575 said:

vonhosen said:

woof said:

Speed cameras ‘increase risk of serious car crashes’ in some areas, RAC claims
http://metro.co.uk/2013/06/07/speed-cameras-increa...

Why did they select only those 551 sites & why has the risk only increased at 21 of those 551 sites?

This is an interesting take on a report done by the RAC and show a good example of a news paper reporting a story in a certain way.

The original RAC report is here:

http://www.racfoundation.org/research/safety/effec...

and the update is here:

http://www.racfoundation.org/research/safety/speed...

What Metro has done is take a part of the report and highlight that as the main news story. They haven't even got the mans name right which doesn't bode well for the standard of reporting.

I'd need to look at the detail of the report to be honest. It could indeed highlight a problem with 21 out of the 551 sites, but given the random nature of accidents i'd be interested to know how many additional crashes took place at these sites to account for the increase.

The overall view of the report though is that on average fatalites and serious collisions fell by 22% at the 551 sites looked at.

I also noticed it was an old story - sorry didn't see that before now !

[RobinOakapple]

Devil2575 said:

Jasandjules said:

Random nature? Surely you mean "caused by exceeding the speed limit"?

Fatalities are falling on the roads due to vehicular safety improvements. Not because of the Scameras.

No, accidents are to a large degree random because they rely on number of unrelated factors coming together. Certain factors increase the risk of having an accident or the severity of it but that doesn't guarantee that one will occur.

That's right.
Rule 1. You can't prevent accidents because if you could they wouldn't happen, and then they wouldn't be accidents

Rule 2. You can't predict accidents either, because if you could, you would prevent them and then you would have to see rule 1.

[mph1977]

RobinOakapple said:

Devil2575 said:

Jasandjules said:

Random nature? Surely you mean "caused by exceeding the speed limit"?

Fatalities are falling on the roads due to vehicular safety improvements. Not because of the Scameras.

No, accidents are to a large degree random because they rely on number of unrelated factors coming together. Certain factors increase the risk of having an accident or the severity of it but that doesn't guarantee that one will occur.

That's right.
Rule 1. You can't prevent accidents because if you could they wouldn't happen, and then they wouldn't be accidents

Rule 2. You can't predict accidents either, because if you could, you would prevent them and then you would have to see rule 1.

the majority of RTCs are not accidents, hence the change in terminology.

[singlecoil]

mph1977 said:

RobinOakapple said:

Devil2575 said:

Jasandjules said:

Random nature? Surely you mean "caused by exceeding the speed limit"?

Fatalities are falling on the roads due to vehicular safety improvements. Not because of the Scameras.

No, accidents are to a large degree random because they rely on number of unrelated factors coming together. Certain factors increase the risk of having an accident or the severity of it but that doesn't guarantee that one will occur.

That's right.
Rule 1. You can't prevent accidents because if you could they wouldn't happen, and then they wouldn't be accidents

Rule 2. You can't predict accidents either, because if you could, you would prevent them and then you would have to see rule 1.

the majority of RTCs are not accidents, hence the change in terminology.

Really, so they are deliberate? I'm surprised to hear that, especially as whichever party chose to crash into the other risks getting hurt him or her self.

[mph1977]

singlecoil said:

mph1977 said:

RobinOakapple said:

Devil2575 said:

Jasandjules said:

Random nature? Surely you mean "caused by exceeding the speed limit"?

Fatalities are falling on the roads due to vehicular safety improvements. Not because of the Scameras.

No, accidents are to a large degree random because they rely on number of unrelated factors coming together. Certain factors increase the risk of having an accident or the severity of it but that doesn't guarantee that one will occur.

That's right.
Rule 1. You can't prevent accidents because if you could they wouldn't happen, and then they wouldn't be accidents

Rule 2. You can't predict accidents either, because if you could, you would prevent them and then you would have to see rule 1.

the majority of RTCs are not accidents, hence the change in terminology.

Really, so they are deliberate? I'm surprised to hear that, especially as whichever party chose to crash into the other risks getting hurt him or her self.

have you taken lessons in being thick or are you just a 'kipper ?

[singlecoil]

mph1977 said:

have you taken lessons in being thick or are you just a 'kipper ?

I anticipated an answer along these lines, but if anybody's being thick, it's you for not realising that trying to give traffic accidents a different name won't change the fact that they are accidents. You can call them something else as well, if you like, collision for instance, but they are still accidents.

It's simple-

Average traffic 'collision'-

Did it happen? Yes

Was it a good, neutral or bad thing? Bad

Did anyone mean for it to happen? No

ACCIDENT

You can read about it here
http://en.wikipedia.org/wiki/Accident