The reason driving faster is more dangerous
Discussion
I've only recently ventured onto this part of PH. I expected plenty of hate for cameras and defense of speeding but wasn't prepared for some of the bizarre claims being made, such as the speed limit not having any relationship to the dangers of the road. Such claims seem to defy basic physics and my own experience of driving/riding for 30 odd years. It would also make all advanced training (which focuses on identifying and managing hazards) wrong.
I've set out what I see as the argument and evidence for the relationship between speed and risk of crashing.
1. First point is that calling crashes "accidents" is very misleading. Crashes are not generally caused by acts of God - almost all crashes are caused by human error. Yes there will be the odd crash because of an unforeseen blow out and the like but the vast majority of crashes are because of driving mistakes. I would split driver error into three main categories:
a) Observation / anticipation errors - failure to read the road and anticipate what is going to happen next (either through not paying attention and/or poor skills and/or slow reactions) - eg not seeing someone coming from the right when turning left and pulling into their path
b) Errors of judgement - failure to make the right decision eg continuing to drive at 70 on the motorway in a thunderstorm
and aqua planning as a result
c) Errors in controlling the car eg not braking hard enough, not swerving around an obstacle, target fixation
Of course, poor driving can exhibit one, two or all three of these at once.
2. The rate of error depends upon a number of factors eg if you are tired you are likely to make more mistakes. However, looking at the first two categories: errors of observation and judgement, how often you make a mistake will be related to how many times you need to make an important observation or make an important decision. This is where the complexity of the road and number of hazards plays a key role. On a straight, empty motorway in the day then there are few if any hazards (something that demands your attention and a correct decision). Consequently the risk of driving on such roads even for poor drivers is low. Increasing speed should also not increase the risk (at least to a measurable amount). On the other hand, driving in town mostly demands constant attention and decisions eg people pulling out at junctions, on coming traffic on your side of the road as they go around parked cars, etc. Increasing the number of hazards, increases the number of opportunities for humans to screw up and given the law of large numbers, eventually someone will make an error that leads to a crash. Where does speed play a role? The faster you drive the greater the demands put on your powers of observation and ability to make the correct judgements. Increasing the difficulty of the task increases the number of errors. This is evident in every other area of life eg look at computer games that rely on reaction speed - as you progress through the game it gets harder as you have to deal with more obstacles at a quicker pace, the early screens at the slow tempo are easy but you die when the pace hots up. Or take tennis. Watch Wimbledon. Do servers get lots of aces on their first serve hit at 140 or on the second serve hit at 100? It is the first serve because the returner has less time to act correctly and get his racquet on the ball. Increasing the speed limit in town from 30 to 40 would inevitably lead to more errors and more errors will lead to more crashes.
3. As well as increasing the number of errors, additional speed will also lead to more crashes because of the third category of error - driver input. Put simply, the faster you are travelling when you are called upon to take action to avoid a crash (brake, swerve, etc) the greater the skill and the faster the action required to do so successfully. Clearly for a given level of skill the higher the speed then the more likely a "situation" will lead to a crash, rather than a near miss.
4. Lastly, the faster you are travelling then the more kinetic energy you have and the greater destructive potential your vehicle has. All else being equal a crash from a higher initial speed will have more serious consequences for yourself and third parties.
In summary, crashes are mainly caused by driver error. The rate of error increases as the difficulty of the task increases.
Roads with more hazards put greater demands on drivers and so they make more errors. Increasing speed also increases difficulty and increases the error rate. Increasing speed on roads with more hazards should show a steeper increase in errors than on roads with few hazards (this is borne out by research). Increasing speed increases driver input error and also increases the severely of crashes. Roads with lots of hazards (eg urban roads) are more inherently dangerous than roads with few hazards eg motorways,
dual carriageways (in terms of consequences, although your risk of a crash on the motorway is lower but the consequences could be more severe as you are travelling faster). A direct correlation exists between speed and risk for crashes for all roads. The strength of that correlation is directly related to the number of hazards. To reduce the number of crashes to an acceptable level whilst trying to keep traffic moving it is therefore appropriate to have different speed levels (via limits) for different roads. None of the preceding is dependent upon what limits society chooses. It only states the obvious that higher limits will inevitably lead to more crashes. How many more crashes and the impact of such crashes are dependent on lots of other factors. Whether additional crashes are acceptable for the benefit of higher limits is a political decision.
No doubt the speeding apologists will come up with nonsense objections rather than trying to deal with each point above.
I've set out what I see as the argument and evidence for the relationship between speed and risk of crashing.
1. First point is that calling crashes "accidents" is very misleading. Crashes are not generally caused by acts of God - almost all crashes are caused by human error. Yes there will be the odd crash because of an unforeseen blow out and the like but the vast majority of crashes are because of driving mistakes. I would split driver error into three main categories:
a) Observation / anticipation errors - failure to read the road and anticipate what is going to happen next (either through not paying attention and/or poor skills and/or slow reactions) - eg not seeing someone coming from the right when turning left and pulling into their path
b) Errors of judgement - failure to make the right decision eg continuing to drive at 70 on the motorway in a thunderstorm
and aqua planning as a result
c) Errors in controlling the car eg not braking hard enough, not swerving around an obstacle, target fixation
Of course, poor driving can exhibit one, two or all three of these at once.
2. The rate of error depends upon a number of factors eg if you are tired you are likely to make more mistakes. However, looking at the first two categories: errors of observation and judgement, how often you make a mistake will be related to how many times you need to make an important observation or make an important decision. This is where the complexity of the road and number of hazards plays a key role. On a straight, empty motorway in the day then there are few if any hazards (something that demands your attention and a correct decision). Consequently the risk of driving on such roads even for poor drivers is low. Increasing speed should also not increase the risk (at least to a measurable amount). On the other hand, driving in town mostly demands constant attention and decisions eg people pulling out at junctions, on coming traffic on your side of the road as they go around parked cars, etc. Increasing the number of hazards, increases the number of opportunities for humans to screw up and given the law of large numbers, eventually someone will make an error that leads to a crash. Where does speed play a role? The faster you drive the greater the demands put on your powers of observation and ability to make the correct judgements. Increasing the difficulty of the task increases the number of errors. This is evident in every other area of life eg look at computer games that rely on reaction speed - as you progress through the game it gets harder as you have to deal with more obstacles at a quicker pace, the early screens at the slow tempo are easy but you die when the pace hots up. Or take tennis. Watch Wimbledon. Do servers get lots of aces on their first serve hit at 140 or on the second serve hit at 100? It is the first serve because the returner has less time to act correctly and get his racquet on the ball. Increasing the speed limit in town from 30 to 40 would inevitably lead to more errors and more errors will lead to more crashes.
3. As well as increasing the number of errors, additional speed will also lead to more crashes because of the third category of error - driver input. Put simply, the faster you are travelling when you are called upon to take action to avoid a crash (brake, swerve, etc) the greater the skill and the faster the action required to do so successfully. Clearly for a given level of skill the higher the speed then the more likely a "situation" will lead to a crash, rather than a near miss.
4. Lastly, the faster you are travelling then the more kinetic energy you have and the greater destructive potential your vehicle has. All else being equal a crash from a higher initial speed will have more serious consequences for yourself and third parties.
In summary, crashes are mainly caused by driver error. The rate of error increases as the difficulty of the task increases.
Roads with more hazards put greater demands on drivers and so they make more errors. Increasing speed also increases difficulty and increases the error rate. Increasing speed on roads with more hazards should show a steeper increase in errors than on roads with few hazards (this is borne out by research). Increasing speed increases driver input error and also increases the severely of crashes. Roads with lots of hazards (eg urban roads) are more inherently dangerous than roads with few hazards eg motorways,
dual carriageways (in terms of consequences, although your risk of a crash on the motorway is lower but the consequences could be more severe as you are travelling faster). A direct correlation exists between speed and risk for crashes for all roads. The strength of that correlation is directly related to the number of hazards. To reduce the number of crashes to an acceptable level whilst trying to keep traffic moving it is therefore appropriate to have different speed levels (via limits) for different roads. None of the preceding is dependent upon what limits society chooses. It only states the obvious that higher limits will inevitably lead to more crashes. How many more crashes and the impact of such crashes are dependent on lots of other factors. Whether additional crashes are acceptable for the benefit of higher limits is a political decision.
No doubt the speeding apologists will come up with nonsense objections rather than trying to deal with each point above.
Welcome to the Dunning-Kruger part of PH ...
it is abundantly clear that many of the people expressing the sentiments you describe / discuss above simply do not know what they do not know and feel so confident in their illusory superiority that they feel they can call people with experience of emergency driving / driver development / policing and health care idiots and bed wetters ...
it is abundantly clear that many of the people expressing the sentiments you describe / discuss above simply do not know what they do not know and feel so confident in their illusory superiority that they feel they can call people with experience of emergency driving / driver development / policing and health care idiots and bed wetters ...
Edited by mph1977 on Thursday 12th May 17:56
Esceptico said:
1. First point is that calling crashes "accidents" is very misleading.
I agree with the rest of what you said, but feel the need to point out that yes, crashes are accidents (whatever their causes) because they are a) negative events and b) unintended. To not be accidents they would need to be intentional.singlecoil said:
Esceptico said:
1. First point is that calling crashes "accidents" is very misleading.
I agree with the rest of what you said, but feel the need to point out that yes, crashes are accidents (whatever their causes) because they are a) negative events and b) unintended. To not be accidents they would need to be intentional.
t happens - couldn't be helped, better luck next time.""Crash" doesn't carry any implication of deliberateness, but removes that implication of "Nowt I could do about it" - which is only right, because in almost every crash there is at least one person who's contributed extensively to it happening. Unwittingly, sure, but still negligent wuckfittery.
Esceptico said:
In summary, crashes are mainly caused by driver error.
Yup.Esceptico said:
The rate of error increases as the difficulty of the task increases.
Yup, with the caveat that that's relative to the ability and the attention of the person performing the task.Esceptico said:
Roads with more hazards put greater demands on drivers and so they make more errors.
Increasing speed also increases difficulty and increases the error rate.
Not so sure about that.Increasing speed also increases difficulty and increases the error rate.
Put somebody onto a boring road at a low speed, and watch their attention wander.
Put somebody onto a road that's clearly hazardous, and tell them to get a wiggle on, and watch them focus.
Esceptico said:
No doubt the speeding apologists...
And there you go, conflating inappropriate speed for the conditions - which I very much doubt ANYBODY would condone - with speed above the limit.If somebody is driving dangerously, charge 'em with dangerous driving.
If somebody is driving carelessly, charge 'em with careless driving.
Both those can, of course, be easily committed within the speed limit.
Which really leaves "exceeding the speed limit" as simply an administrative "one-number-bigger-than-another-number" comparison, with absolute zero implication on the risks present.
It's just not that simple though. I agree that going 'too fast' is dangerous, this is an completely unrelated concept to 'exceeding the speed limit'.
I agree that if you take a busy pedestrianised area and plot a chart of the speed of a car driving through it vs the probability of a collision there will be a clear and unarguable correlation between the two. If however you take a four lane motorway at midnight and plot the same chart it will not show such a correlation until a certain threshold speed has been exceeded, i.e. driving down a motorway at 10mph is not measurably safer than driving down it at 20mph but driving down it at 100mph is clearly safer than at 200mph.
The crux of my argument is that there is a threshold speed at which the risk is negligibly small, going slower than this will yield no increase in safety, above this speed there is a clear correlation of danger to speed as you describe. The posted speed limit sometimes bears some resemblance to this safe speed threshold but more often than not it does not, therefore to make a blanket claim that 'exceeding the speed limit is dangerous' is clearly false. Sometimes it is, sometimes it isn't, ever more so now that politics, council NIMBYism and 'environmentalism' are allowed to set ever lower limits everywhere that have nothing to do with safety.
^^^^^ Also what TooMany2CVs said
I agree that if you take a busy pedestrianised area and plot a chart of the speed of a car driving through it vs the probability of a collision there will be a clear and unarguable correlation between the two. If however you take a four lane motorway at midnight and plot the same chart it will not show such a correlation until a certain threshold speed has been exceeded, i.e. driving down a motorway at 10mph is not measurably safer than driving down it at 20mph but driving down it at 100mph is clearly safer than at 200mph.
The crux of my argument is that there is a threshold speed at which the risk is negligibly small, going slower than this will yield no increase in safety, above this speed there is a clear correlation of danger to speed as you describe. The posted speed limit sometimes bears some resemblance to this safe speed threshold but more often than not it does not, therefore to make a blanket claim that 'exceeding the speed limit is dangerous' is clearly false. Sometimes it is, sometimes it isn't, ever more so now that politics, council NIMBYism and 'environmentalism' are allowed to set ever lower limits everywhere that have nothing to do with safety.
^^^^^ Also what TooMany2CVs said
Edited by TurboHatchback on Thursday 12th May 18:19
TooMany2cvs said:
singlecoil said:
Esceptico said:
1. First point is that calling crashes "accidents" is very misleading.
I agree with the rest of what you said, but feel the need to point out that yes, crashes are accidents (whatever their causes) because they are a) negative events and b) unintended. To not be accidents they would need to be intentional.t happens - couldn't be helped, better luck next time.""Crash" doesn't carry any implication of deliberateness, but removes that implication of "Nowt I could do about it" - which is only right, because in almost every crash there is at least one person who's contributed extensively to it happening. Unwittingly, sure, but still negligent wuckfittery.
Start with any decent dictionary, and have a look at this too
https://en.wikipedia.org/wiki/Accident
Hope that helps.
I would agree with a fair bit of what you said, however, there is one item that, to a point, disagrees with your overall point. That is the level of attention and concentration given to the task of driving.
In general drive too slowly for the conditions and your concentration will slip because you do effectively 'get bored'. In the nearly 40 years and approximately 600,000 miles of driving I have done I have noticed that there is what I term a safe speed to travel at. This is the speed where you are concentrating fully on the task at hand but are not travelling too fast for the conditions.
This 'safe speed' will vary for any given section of road dependent on a variety of things, such as weather, traffic, even the vehicle you are driving. As a regular cross-continent driver I found that on the de-restricted autobahns the safe speed varied greatly. For example, in similar weather and traffic conditions the safe speed varied based on what car/HGV I was driving, it was higher in my A6 and, at the time, Ferrari compared to my Skoda Octavia.
For me the concentration level goes up with speed, but reaches a plateau before concern then rises. Too much concern means you are going too fast.
In this country with our crowded roads and relatively low level of driver skill any speed much over 75 (on a motorway) is too high in general day to day conditions. This is based on the simple fact that a large number of drivers pay little attention and are highly likely to pull out straight in front of you. In Germany this is much less prevalent because the drivers expect people to be going faster than they are.
In summary you are more likely to have a collision if you are driving too slowly than if you are driving at the safe speed for the conditions.
Speed will obviously have an effect on the outcome, however, based on lots of professional analysis over the years, excess speed is only the cause of around 5% of all collisions. Should we not concentrate on other causes before blindly going down the speed kills route? Improve driver awareness and skills by 20% and you would cut down on more collisions than by cutting speeds by 20%.
In general drive too slowly for the conditions and your concentration will slip because you do effectively 'get bored'. In the nearly 40 years and approximately 600,000 miles of driving I have done I have noticed that there is what I term a safe speed to travel at. This is the speed where you are concentrating fully on the task at hand but are not travelling too fast for the conditions.
This 'safe speed' will vary for any given section of road dependent on a variety of things, such as weather, traffic, even the vehicle you are driving. As a regular cross-continent driver I found that on the de-restricted autobahns the safe speed varied greatly. For example, in similar weather and traffic conditions the safe speed varied based on what car/HGV I was driving, it was higher in my A6 and, at the time, Ferrari compared to my Skoda Octavia.
For me the concentration level goes up with speed, but reaches a plateau before concern then rises. Too much concern means you are going too fast.
In this country with our crowded roads and relatively low level of driver skill any speed much over 75 (on a motorway) is too high in general day to day conditions. This is based on the simple fact that a large number of drivers pay little attention and are highly likely to pull out straight in front of you. In Germany this is much less prevalent because the drivers expect people to be going faster than they are.
In summary you are more likely to have a collision if you are driving too slowly than if you are driving at the safe speed for the conditions.
Speed will obviously have an effect on the outcome, however, based on lots of professional analysis over the years, excess speed is only the cause of around 5% of all collisions. Should we not concentrate on other causes before blindly going down the speed kills route? Improve driver awareness and skills by 20% and you would cut down on more collisions than by cutting speeds by 20%.
TooMany2cvs said:
Esceptico said:
In summary, crashes are mainly caused by driver error.
Yup.Esceptico said:
The rate of error increases as the difficulty of the task increases.
Yup, with the caveat that that's relative to the ability and the attention of the person performing the task.Esceptico said:
Roads with more hazards put greater demands on drivers and so they make more errors.
Increasing speed also increases difficulty and increases the error rate.
Not so sure about that.Increasing speed also increases difficulty and increases the error rate.
Put somebody onto a boring road at a low speed, and watch their attention wander.
Put somebody onto a road that's clearly hazardous, and tell them to get a wiggle on, and watch them focus.
That might be true for some people some of the time. Crash statistics reflect what very many people do, with lots of different attitudes towards driving over long periods of time. Your exception will have little or no real impact overall. It is also not really true. Just ask yourself how many people you see using their phones in town whilst driving where they should be concentrating
Esceptico said:
No doubt the speeding apologists...
And there you go, conflating inappropriate speed for the conditions - which I very much doubt ANYBODY would condone - with speed above the limit.If somebody is driving dangerously, charge 'em with dangerous driving.
If somebody is driving carelessly, charge 'em with careless driving.
Both those can, of course, be easily committed within the speed limit.
Which really leaves "exceeding the speed limit" as simply an administrative "one-number-bigger-than-another-number" comparison, with absolute zero implication on the risks present.
TurboHatchback said:
It's just not that simple though. I agree that going 'too fast' is dangerous, this is an completely unrelated concept to 'exceeding the speed limit'.
I agree that if you take a busy pedestrianised area and plot a chart of the speed of a car driving through it vs the probability of a collision there will be a clear and unarguable correlation between the two. If however you take a four lane motorway at midnight and plot the same chart it will not show such a correlation until a certain threshold speed has been exceeded, i.e. driving down a motorway at 10mph is not measurably safer than driving down it at 20mph but driving down it at 100mph is clearly safer than at 200mph.
The crux of my argument is that there is a threshold speed at which the risk is negligibly small, going slower than this will yield no increase in safety, above this speed there is a clear correlation of danger to speed as you describe. The posted speed limit sometimes bears some resemblance to this safe speed threshold but more often than not it does not, therefore to make a blanket claim that 'exceeding the speed limit is dangerous' is clearly false. Sometimes it is, sometimes it isn't, ever more so now that politics, council NIMBYism and 'environmentalism' are allowed to set ever lower limits everywhere that have nothing to do with safety.
^^^^^ Also what TooMany2CVs said
As noted above in my response to TooMany2CVs, one person speeding won't increase the crash rate but large numbers of people doing so will. To try to stop large numbers of people speeding there has to be a deterrent (unless you can persuade them not to do it of their own accord - drink driving has been attacked by both stiffer punishment but also by trying to make it socially unacceptable. They are trying to do the same with speeding). Punishing individuals speeders is not because their actions were necessary dangerous but rather to try to stop a large number of people speeding.I agree that if you take a busy pedestrianised area and plot a chart of the speed of a car driving through it vs the probability of a collision there will be a clear and unarguable correlation between the two. If however you take a four lane motorway at midnight and plot the same chart it will not show such a correlation until a certain threshold speed has been exceeded, i.e. driving down a motorway at 10mph is not measurably safer than driving down it at 20mph but driving down it at 100mph is clearly safer than at 200mph.
The crux of my argument is that there is a threshold speed at which the risk is negligibly small, going slower than this will yield no increase in safety, above this speed there is a clear correlation of danger to speed as you describe. The posted speed limit sometimes bears some resemblance to this safe speed threshold but more often than not it does not, therefore to make a blanket claim that 'exceeding the speed limit is dangerous' is clearly false. Sometimes it is, sometimes it isn't, ever more so now that politics, council NIMBYism and 'environmentalism' are allowed to set ever lower limits everywhere that have nothing to do with safety.
^^^^^ Also what TooMany2CVs said
Edited by TurboHatchback on Thursday 12th May 18:19
Esceptico said:
You haven't really followed the argument. An individual speeding may not represent an increased risk. Millions of people speeding will definitely increase the number of crashes. That is why there are limits and why they are enforced.
It makes whatsoever no difference to my argument whether we're talking about an individual or every single road user.
i have absolutely no statistics, but i reckon we need more policing of:
- phone usage
- driving without due care and attention (plenty of examples daily of people searching handbags, eating, veering all over)
- aggressive driving (technically reckless?)
as a driving god i like to exceed the speed limit where possible and appropriate. Maybe that's a little reckless, but i don't have any close shaves at all. Plenty when younger, i fully admit. Not that the law stops youth taking its path. I recognise most 20mph and 30mph zones as being warranted, sensible and i comply willingly. cameras or not. Some 40 and 50 zones are clearly H&S taking the easy, money earning path. Most drivers are insufficiently trained and/or aware. But that's not going to change, so speed limits and cameras are the easy option.
- phone usage
- driving without due care and attention (plenty of examples daily of people searching handbags, eating, veering all over)
- aggressive driving (technically reckless?)
as a driving god i like to exceed the speed limit where possible and appropriate. Maybe that's a little reckless, but i don't have any close shaves at all. Plenty when younger, i fully admit. Not that the law stops youth taking its path. I recognise most 20mph and 30mph zones as being warranted, sensible and i comply willingly. cameras or not. Some 40 and 50 zones are clearly H&S taking the easy, money earning path. Most drivers are insufficiently trained and/or aware. But that's not going to change, so speed limits and cameras are the easy option.
Esceptico said:
I've only recently ventured onto this part of PH. I expected plenty of hate for cameras and defense of speeding but wasn't prepared for some of the bizarre claims being made, such as the speed limit not having any relationship to the dangers of the road.
I'm not reading the rest of that, but I assume the existence of this thread means you never did work out what a direct correlation is in that other thread.Gassing Station | Speed, Plod & the Law | Top of Page | What's New | My Stuff