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#21
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UK cyclists kill or maim two people a week
On 13/10/17 14:04, Nick wrote:
FWIW the effect you are talking about with respect urban/non urban trips is called Simpson's Paradox. https://en.wikipedia.org/wiki/Simpson%27s_paradox Thanks for that. |
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#22
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UK cyclists kill or maim two people a week
On Friday, October 13, 2017 at 2:04:43 PM UTC+1, Nick wrote:
On 13/10/2017 00:28, TMS320 wrote: On 12/10/17 22:11, Peter Parry wrote: On Thu, 12 Oct 2017 01:07:40 +0100, TMS320 wrote: On 11/10/17 12:28, Peter Parry wrote: On Wed, 11 Oct 2017 10:20:28 +0100, TMS320 wrote: On 11/10/17 09:35, Peter Parry wrote: On Tue, 10 Oct 2017 12:06:02 -0700 (PDT), Simon Jester Do these figure take into account that the majority of car miles are on trunk roads where there are few, if any, pedestrians? Whilst bicycles spend most of their time in urban environments. If not then they are worthless. They do. On urban roads Pushbikes seriously injure 26 pedestrians per billion km and kill 0.5, cars seriously injure 10 and kill 0.7.. So you love to push this. "Push"?Â* One mention of DfT statistics is pushing them? Yes. You have brought this up several times before. It is obvious you think it is meaningful. It is clearly meaningful as it is the data used by the government to make decisions. I asked you why you think pedestrian casualties per vehicle-distance is meaningful. Don't evade the question. Of course it is. That doesn't answer the question. You won't get an answer. He won't even attempt an answer because he knows he isn't clever enough. FWIW the effect you are talking about with respect urban/non urban trips is called Simpson's Paradox. https://en.wikipedia.org/wiki/Simpson%27s_paradox So what metric should we use? Passanger miles don't count because there is only one driver per vehicle. |
#23
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UK cyclists kill or maim two people a week
On 14/10/2017 15:08, Simon Jester wrote:
I asked you why you think pedestrian casualties per vehicle-distance is meaningful. Don't evade the question. Of course it is. That doesn't answer the question. You won't get an answer. He won't even attempt an answer because he knows he isn't clever enough. FWIW the effect you are talking about with respect urban/non urban trips is called Simpson's Paradox. https://en.wikipedia.org/wiki/Simpson%27s_paradox So what metric should we use? Passanger miles don't count because there is only one driver per vehicle. A suitable metric depends on the question being asked. There is no general purpose correct metric that is useful for every question. You might just as well ask if I want to buy something from a shop, how much should I pay? Presumably Peter wanted to suggest that the statistics showed that cyclists posed as great a risk to pedestrians as motorists but this almost certainly isn't true, either in absolute terms or in terms of per utility unit for any sensible utility unit I can think of. On usenet it is frightening to so how many people misunderstand basic scientific/mathematical/statistical arguments. Cycle helmets, cycle paths, global warming, vaccines. Even people who should know better quote stupid ******** as if it means something. |
#24
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UK cyclists kill or maim two people a week
On 14/10/17 15:08, Simon Jester wrote:
On Friday, October 13, 2017 at 2:04:43 PM UTC+1, Nick wrote: On 13/10/2017 00:28, TMS320 wrote: On 12/10/17 22:11, Peter Parry wrote: On Thu, 12 Oct 2017 01:07:40 +0100, TMS320 wrote: On 11/10/17 12:28, Peter Parry wrote: On Wed, 11 Oct 2017 10:20:28 +0100, TMS320 wrote: On 11/10/17 09:35, Peter Parry wrote: On Tue, 10 Oct 2017 12:06:02 -0700 (PDT), Simon Jester Do these figure take into account that the majority of car miles are on trunk roads where there are few, if any, pedestrians? Whilst bicycles spend most of their time in urban environments. If not then they are worthless. They do. On urban roads Pushbikes seriously injure 26 pedestrians per billion km and kill 0.5, cars seriously injure 10 and kill 0.7. So you love to push this. "Push"?Â* One mention of DfT statistics is pushing them? Yes. You have brought this up several times before. It is obvious you think it is meaningful. It is clearly meaningful as it is the data used by the government to make decisions. I asked you why you think pedestrian casualties per vehicle-distance is meaningful. Don't evade the question. Of course it is. That doesn't answer the question. You won't get an answer. He won't even attempt an answer because he knows he isn't clever enough. FWIW the effect you are talking about with respect urban/non urban trips is called Simpson's Paradox. https://en.wikipedia.org/wiki/Simpson%27s_paradox So what metric should we use? Passanger miles don't count because there is only one driver per vehicle. Passenger miles isn't too bad - even if there is a passenger variation from 1 to 5; at least they're actually inside the vehicles that are doing the miles. (I expect Simpson's paradox would find a strange result between 1 occupant, 5 occupants and average occupancy - whatever that average is.) I just canot fathom out why there is supposed to be a link between pedestrians and vehicle miles. |
#25
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UK cyclists kill or maim two people a week
On Saturday, October 14, 2017 at 8:43:52 PM UTC+1, Nick wrote:
On 14/10/2017 15:08, Simon Jester wrote: I asked you why you think pedestrian casualties per vehicle-distance is meaningful. Don't evade the question. Of course it is. That doesn't answer the question. You won't get an answer. He won't even attempt an answer because he knows he isn't clever enough. FWIW the effect you are talking about with respect urban/non urban trips is called Simpson's Paradox. https://en.wikipedia.org/wiki/Simpson%27s_paradox So what metric should we use? Passanger miles don't count because there is only one driver per vehicle. A suitable metric depends on the question being asked. There is no general purpose correct metric that is useful for every question. The question becomes what question do we ask? You might just as well ask if I want to buy something from a shop, how much should I pay? Presumably Peter wanted to suggest that the statistics showed that cyclists posed as great a risk to pedestrians as motorists but this almost certainly isn't true, either in absolute terms or in terms of per utility unit for any sensible utility unit I can think of. Seen it all before. Hugh Davies and Steve Firth come to mind. On usenet it is frightening to so how many people misunderstand basic scientific/mathematical/statistical arguments. Cycle helmets, cycle paths, global warming, vaccines. Even people who should know better quote stupid ******** as if it means something. You are more likely to be killed by a blue car than a green car. |
#26
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UK cyclists kill or maim two people a week
On Saturday, October 14, 2017 at 8:43:56 PM UTC+1, TMS320 wrote:
On 14/10/17 15:08, Simon Jester wrote: On Friday, October 13, 2017 at 2:04:43 PM UTC+1, Nick wrote: On 13/10/2017 00:28, TMS320 wrote: On 12/10/17 22:11, Peter Parry wrote: On Thu, 12 Oct 2017 01:07:40 +0100, TMS320 wrote: On 11/10/17 12:28, Peter Parry wrote: On Wed, 11 Oct 2017 10:20:28 +0100, TMS320 wrote: On 11/10/17 09:35, Peter Parry wrote: On Tue, 10 Oct 2017 12:06:02 -0700 (PDT), Simon Jester Do these figure take into account that the majority of car miles are on trunk roads where there are few, if any, pedestrians? Whilst bicycles spend most of their time in urban environments. If not then they are worthless. They do. On urban roads Pushbikes seriously injure 26 pedestrians per billion km and kill 0.5, cars seriously injure 10 and kill 0..7. So you love to push this. "Push"?Â* One mention of DfT statistics is pushing them? Yes. You have brought this up several times before. It is obvious you think it is meaningful. It is clearly meaningful as it is the data used by the government to make decisions. I asked you why you think pedestrian casualties per vehicle-distance is meaningful. Don't evade the question. Of course it is. That doesn't answer the question. You won't get an answer. He won't even attempt an answer because he knows he isn't clever enough. FWIW the effect you are talking about with respect urban/non urban trips is called Simpson's Paradox. https://en.wikipedia.org/wiki/Simpson%27s_paradox So what metric should we use? Passanger miles don't count because there is only one driver per vehicle. Passenger miles isn't too bad - even if there is a passenger variation from 1 to 5; at least they're actually inside the vehicles that are doing the miles. (I expect Simpson's paradox would find a strange result between 1 occupant, 5 occupants and average occupancy - whatever that average is.) If I drive my car on a given mile of road on my own I pose 5x as much danger to other road users than if I drive the same mile with 4 passengers, that is what passenger miles tells us. |
#27
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UK cyclists kill or maim two people a week
On 14/10/17 23:26, Simon Jester wrote:
On Saturday, October 14, 2017 at 8:43:56 PM UTC+1, TMS320 wrote: On 14/10/17 15:08, Simon Jester wrote: So what metric should we use? Passanger miles don't count because there is only one driver per vehicle. Passenger miles isn't too bad - even if there is a passenger variation from 1 to 5; at least they're actually inside the vehicles that are doing the miles. (I expect Simpson's paradox would find a strange result between 1 occupant, 5 occupants and average occupancy - whatever that average is.) If I drive my car on a given mile of road on my own I pose 5x as much danger to other road users than if I drive the same mile with 4 passengers, that is what passenger miles tells us. No. I understood your passenger miles to mean occupant casualties per vehicle distance. If the number reduces (so long as average number of people carried per vehicle has not reduced), it is generally considered to be good development. |
#28
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UK cyclists kill or maim two people a week
On Mon, 16 Oct 2017 22:15:16 +0100, TMS320 wrote:
On 15/10/17 18:35, Peter Parry wrote: On Fri, 13 Oct 2017 00:28:39 +0100, TMS320 wrote: On 12/10/17 22:11, Peter Parry wrote: On Thu, 12 Oct 2017 01:07:40 +0100, TMS320 wrote: Safety (incidence rate) is the quotient of the number of fatalities/injuries divided by the measure of exposure (trips/miles/hours). When the terms are make sense. Vehicle occupants per vehicle distance does. Pedestrians per vehicle distance does not. In a vehicle/pedestrian impact I'm not sure why you think there is a meaningful difference if the car has a driver and three passengers compared with a driver alone. Whether you look at impacts per pedestrian or impact per vehicle the result is going to be the same. For whatever reason the DfT have chosen to use distance as the measure of exposure. The problem of course is that no matter what you chose if it is inadequately measured or missing altogether it forms a poor basis for planning the future. Government departments are not unknown to measure apples and pears and ending up with oranges. You haven't answered the question of why you think vehicle-distance is meaningful to pedestrians. You have to have a common base to allow for the detection of trends. Looking for impacts per pedestrian mile or impacts per pushbike mile is going to produce the same result.Why they chose the measurement they have I do not know - but it seems to be used by many road transport investigators worldwide. Let's try to be more specific. Let's hypothesise that a significant proportion of pedestrians suddenly stopped walking. We don't know the original population or the proportion but we would probably see casualties per vehicle-distance to reduce. Does it inform us whether the people that continued to walk are more or less safe? As long as you have an adequate supply of targets the accident per unit of distance is sound. If your pedestrian population is exposed to all the threats you are trying to assess then accidents per x miles is as valid as any other measure and better than most others. It isn't sound when targets are unrelated. The targets are not unrelated. The vehicles (whether cars or pushbikes) are operating in an environment containing similar numbers of pedestrians. The absolute numbers of accidents per unit of distance may differ between urban and rural settings and the ratio of accidents between pushbikes/pedestrians and cars/pedestrians may alter between rural and urban settings but these a captured in RAS30018. The simplest way of stopping all bicycle related accidents whether vehicle bike or pedestrian bike is to ban bicycling. Overnight the number drops to zero. However, accident reduction has to take into account the benefit of the mode of transport as well as the cost. If cycling was banned the pedestrian casualties would move across to motor vehicles. Not necessarily, many cycle/pedestrian accidents involve cyclist traveling fast on the inside of a slow traffic stream and impacting pedestrians stepping out from behind obstructions in the expectation there will be a space there only to find the space contains a cyclist at speed. Similarly in cities cyclists often ignore pedestrian crossings and weave between crossing pedestrians. Pedestrians also often ignore cyclists when crossing the road whereas they would not risk confrontation with a car. It is by no means certain that accidents would simply transfer from bikes to cars. Given the death to injury ratio, we also know that cycle related injuries are, in general, less severe. At slow speeds it isn't necessarily so. In cities Pushbikes often travel faster than cars and whereas cars are designed to give some degree of pedestrian protection in an accident pushbikes are not. Indeed some pushbikes sport potentially lethal modifications such as aerobars, Bullhorn bars and bar ends. Cars are also quicker to stop than bikes thus avoiding an accident altogether. It is a fact that cyclist cause more serious injuries to pedestrians than cars per distance traveled. It is highly probable that far more pushbike/pedestrian accidents occur than are reported. It is almost certain that the number of injuries to pedestrians by cyclists is grossly under reported. You emphasise accuracy of injury reporting but make no mention of accuracy of distance reporting. All of the data collection concerning cycling accidents is inaccurate. The main impact is seen in the often poor design of measures meant to reduce pushbike casualties. |
#29
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UK cyclists kill or maim two people a week
On 17/10/17 14:49, Peter Parry wrote:
On Mon, 16 Oct 2017 22:15:16 +0100, TMS320 wrote: On 15/10/17 18:35, Peter Parry wrote: On Fri, 13 Oct 2017 00:28:39 +0100, TMS320 wrote: On 12/10/17 22:11, Peter Parry wrote: On Thu, 12 Oct 2017 01:07:40 +0100, TMS320 wrote: Safety (incidence rate) is the quotient of the number of fatalities/injuries divided by the measure of exposure (trips/miles/hours). When the terms are make sense. Vehicle occupants per vehicle distance does. Pedestrians per vehicle distance does not. In a vehicle/pedestrian impact I'm not sure why you think there is a meaningful difference if the car has a driver and three passengers compared with a driver alone. I wasn't intentionally connecting vehicle occupants to pedestrian casualties. I should have said vehicle occupant casualties per vehicle distance. The cost/benefit of the journey goes to the occupants. Whether you look at impacts per pedestrian or impact per vehicle the result is going to be the same. For whatever reason the DfT have chosen to use distance as the measure of exposure. The problem of course is that no matter what you chose if it is inadequately measured or missing altogether it forms a poor basis for planning the future. Government departments are not unknown to measure apples and pears and ending up with oranges. You haven't answered the question of why you think vehicle-distance is meaningful to pedestrians. You have to have a common base to allow for the detection of trends. Looking for impacts per pedestrian mile or impacts per pushbike mile is going to produce the same result.Why they chose the measurement they have I do not know - but it seems to be used by many road transport investigators worldwide. The French look at it by population... As I said, their figures show no connection between casualties and vehicle distance, pedestrian or occupant. The only feature that connects with distance travelled is that the occupant fatal/injury ratio rises. Perhaps this suggests that trips over longer distances mean there crashes occur at higher speeds and there is more likelyhood of the driver falling asleep. Let's try to be more specific. Let's hypothesise that a significant proportion of pedestrians suddenly stopped walking. We don't know the original population or the proportion but we would probably see casualties per vehicle-distance to reduce. Does it inform us whether the people that continued to walk are more or less safe? As long as you have an adequate supply of targets the accident per unit of distance is sound. If your pedestrian population is exposed to all the threats you are trying to assess then accidents per x miles is as valid as any other measure and better than most others. It isn't sound when targets are unrelated. The targets are not unrelated. The vehicles (whether cars or pushbikes) are operating in an environment containing similar numbers of pedestrians. The absolute numbers of accidents per unit of distance may differ between urban and rural settings and the ratio of accidents between pushbikes/pedestrians and cars/pedestrians may alter between rural and urban settings but these a captured in RAS30018. We have to disagree. The simplest way of stopping all bicycle related accidents whether vehicle bike or pedestrian bike is to ban bicycling. Overnight the number drops to zero. However, accident reduction has to take into account the benefit of the mode of transport as well as the cost. If cycling was banned the pedestrian casualties would move across to motor vehicles. Not necessarily, many cycle/pedestrian accidents involve cyclist traveling fast on the inside of a slow traffic stream and impacting pedestrians stepping out from behind obstructions in the expectation there will be a space there only to find the space contains a cyclist at speed. Similarly in cities cyclists often ignore pedestrian crossings and weave between crossing pedestrians. Pedestrians also often ignore cyclists when crossing the road whereas they would not risk confrontation with a car. It is by no means certain that accidents would simply transfer from bikes to cars. If cycling was banned the ex-riders would not disappear off the face of the earth. Some would become pedestrians producing pedestrian casualties, some would increase the number of cars, causing pedestrian casualties. Given the death to injury ratio, we also know that cycle related injuries are, in general, less severe. At slow speeds it isn't necessarily so. In cities Pushbikes often travel faster than cars and whereas cars are designed to give some degree of pedestrian protection in an accident pushbikes are not. Indeed some pushbikes sport potentially lethal modifications such as aerobars, Bullhorn bars and bar ends. Cars are also quicker to stop than bikes thus avoiding an accident altogether. Bikes are better for going round thus avoiding an accident. The death to injury ratio (RAS30018 Reported casualties sheet), removing the vehicle-distance element, is the only thing that provides us with an indication of the severity of non-fatal injuries in a collision, ie, if a smaller proportion of injuries convert to death, there must be fewer life threatening injuries in the mix. Where injuries are under reported the ratio improves. You provide only speculation. Pedestrian fatal/serious ratio:- Urban A road Urban other cycle - 2.38% 2.56% mcycl - 2.86% 6.02% car - 7.9% 3.89% bus - 11.49% 15.5% van - 10.00% 6.37% hgv - 53.59% 33.3% (The ratio for motorcycles on A roads is a curious one though.) It is a fact that cyclist cause more serious injuries to pedestrians than cars per distance traveled. It is highly probable that far more pushbike/pedestrian accidents occur than are reported. It is almost certain that the number of injuries to pedestrians by cyclists is grossly under reported. You emphasise accuracy of injury reporting but make no mention of accuracy of distance reporting. All of the data collection concerning cycling accidents is inaccurate. The main impact is seen in the often poor design of measures meant to reduce pushbike casualties. There measures are more likely to be political and nothing to do with data. |
#30
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UK cyclists kill or maim two people a week
On Wed, 18 Oct 2017 09:37:51 +0100, TMS320 wrote:
On 17/10/17 14:49, Peter Parry wrote: On Mon, 16 Oct 2017 22:15:16 +0100, TMS320 wrote: On 15/10/17 18:35, Peter Parry wrote: On Fri, 13 Oct 2017 00:28:39 +0100, TMS320 You have to have a common base to allow for the detection of trends. Looking for impacts per pedestrian mile or impacts per pushbike mile is going to produce the same result.Why they chose the measurement they have I do not know - but it seems to be used by many road transport investigators worldwide. The French look at it by population... As I said, their figures show no connection between casualties and vehicle distance, pedestrian or occupant. A vehicle/bike/pedestrian is exposed to the risk of an accident whenever it is on the road. It would be surprising if the likelihood of an event turned out to be unrelated to the exposure to the risk be that in terms of miles traveled or hours driving/walking etc. You can certainly use the overall measure of accidents per million inhabitants per year to see if large scale policies are having an overall effect and you could use the same measure for groups within the whole - what you cannot do is use the measure of accidents per million inhabitants to compare the relative probability of an accident across multiple groups. The French appear to use accidents/million population for overall figures and accidents/million km for comparative purposes (for example comparing accidents attributed to foreign drivers against locals). They also use accidents per hour when looking at relative risks. They also lament the poor quality of data collection "Accidents with pedal cyclists who were hospitalised are very under estimated in the national register of accidents particularly as the police and gendarmerie are not always called to these accidents especially if no motorist is involved." The death to injury ratio (RAS30018 Reported casualties sheet), removing the vehicle-distance element, is the only thing that provides us with an indication of the severity of non-fatal injuries in a collision, The severity of injury data for more serious injuries at is available in hospital admission data and has certainly been included is some studies. if a smaller proportion of injuries convert to death, there must be fewer life threatening injuries in the mix. Which has no relationship with causation. You emphasise accuracy of injury reporting but make no mention of accuracy of distance reporting. All of the data collection concerning cycling accidents is inaccurate. The main impact is seen in the often poor design of measures meant to reduce pushbike casualties. There measures are more likely to be political and nothing to do with data. Politicians are not noted for their intelligence and their general mantra is "Don't just stand there - do something" where "something" can bear no relationship to the problem. They tend to be overly influenced by shouty lobby groups (who are also rarely interested in the truth, their mind is made up and they don't want to be confused by facts). The civil servants who do make up the briefing papers would dearly like better facts as they generally do like getting the right answer. |
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