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That's brilliant Pete. All those things I've been thinking about are covered by the factor you apply to t. Analysing each one in turn may tell you which way they'll nudge the factor, and perhaps by roughly how much. But in real life they're mostly unknown at the critical point in time. That of course makes things very unpredictable. It would even describe situations where the impact speed is greater than the inital speed if you allow negative values for the factor applied to t.

I think we had our wires crossed all this time because my thinking only applies when analysing it after the event, which I don't think I ever said. . You're right that we can't know in advance how large an effect these things will have. However, I do think we still need to look at things after the event to see which factors play a greater part.

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Make everything as simple as possible, but not simpler - Einstein

Peter,

Yes I follow your reasoning better and agree that your argument that "i" is unpredictable applies for a single event. However, the range of possible values for "i" is between 0 and "s" so the greater the value of "s", the greater the possible value of "i". That is a relationship.

Sets of random numbers have even distributions. In 25% of cases, t is zero. This is not an even distribution. Therefore, t is not random.

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I stole this .sig

Yes, but given that, in the majority of cases, a) most pedestrians/drivers aren't suicidal/homicidal, b) most are fairly alert, and c) possibly most importantly, particularly pedestrians, usually take a fair amount of time to get from where you first see them to when they're within your path (they hardly ever 'just appear out of nowhere' - unless you're inattentive), t will tend to be closer to 1 than it is to 0.
Especially given that even a fraction of a second on the brake pedal will scrub off several mph.

Regards
Peter

I think we've done this to death. I am largely persuaded that initial free travelling speed is not the most important of the factors that determine impact speed. I'm sure you are too. We may have different reasons for holding that view but so be it.

I can always host images at Safe Speed. Just send it along by email.

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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

Thanks Paul. I think I'll do that.

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Make everything as simple as possible, but not simpler - Einstein

I've been sketching this flow chart out over the last couple of days to see if I could get a handle on what order of importance various factors have on severity. This is the presentable version without the fag ash and coffee marks, but with legible writing. An arrow shows that a factor affects the one it's pointing to, so nearer the top is more important, nearer the bottom is less important. Solid lines go to the "Severity" box as it's the result not a factor. This isn't relative importance by the way, just an attempt to show what order of importance various factors fall into.

You'll see I've got "Initial speed" about halfway up. It occurred to me that this is a funny one as it directly affects two other factors - distance covered during reaction time and distance covered while braking. I'm now thinking that this makes it more important than I had first thought. My thinking is that anything that affects the point on the road where the brakes are applied is more important than something that does not. The initial speed does affect this a bit in that more distance is covered in the reaction time if it's higher. However, it's not a large effect at normal speeds and is also fairly predictable. That makes it much less important than a driver condition that might dull reaction time, or spotting the hazard early and so braking much earlier.

"Driver's physical condition" is absolutely anything about the driver that will increase or decrease his reaction time and time taken to spot the hazard. That includes effects of drugs/alcohol/medication, kids in back seat jumping up and down and any other distractions, uncorrected eyesight defects, any disease or disorder that may delay response (I'm thinking of an elderly relative with Parkinson's that used to crash about twice a year until the family persuaded him to quit driving). It would also include beneficial effects, such as a driver's experience telling him something was wrong and leading him to cover the brake.

"Condition of vehicle" is similar and includes things like modifications to improve braking performance, neglected maintenance making it worse, boot full of bricks changing the weight and balance and so on. I'm also including the type of vehicle and fitted equipment as that would also change the outcome. This is another one like the initial speed that can affect both braking distance and how severe the impact is. Hit a wall really hard and there may be a difference if you've got an airbag, and from a pedestrians point of view different bonnet designs might make a difference even if by some wild coincidence the amount of energy involved is exactly the same.

"Condition of road" is pretty similar - black ice, new surface, fuel or other vehicle fluids to skid on, high friction surface or normal tarmac, scalped for resurfacing, blahblahblah.

Ta Paul for hosting the image.

Offered up for any thoughts. Is there a reason to move a factor up or down? Have I missed any that might change things? FWIW I think "Condition of road" and "Condition of car" probably shouldn't be of equal importance as I've done it here. I'm leaning towards the car being more important as it's design could make a big difference to either the occupants or anyone being hit.

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Make everything as simple as possible, but not simpler - Einstein

That's very interesting Gatsobait.

I'd love to see some other factors included.

* Driver's mental condition / attention / inattention / distraction

* Luck. During the hazard perception phase we scan the scene ahead. Even when we're attentive and aware, there's chance involved in the exact moment when our attention "passes over" the hazard.

* Time hazard starts. Hazard perception must always come after this.

* Inputs to pre-incident speed. First is general conditions, second is local danger.

* Big inputs to road condition. Especially hills and rain/dry.

* Barriers to hazard perception (poor visibility for example).

Perhaps we should have a specific hazard perception "ding" moment somewhere in the middle? (Maybe left to right middle?) It seems to me that everything here fits into two classes - before hazard perception and after hazard perception.

I think it's slightly optimistic to try to get the importance ranking at this stage. Clearly there will be different importance rankings for different crash developments. It'd be great to get true average rankings, but I don't feel ready to make some of the finer judgements.

Have you got a good facility for editing / redrafting? (Anyone got a good flow charting programme to recommend?)

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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

All included in "Driver's physical condition". Okay, including mental condition etc is stretching the English language a bit, but I was looking for a catch-all term that would cover every possible facet of the driver's current state. Perhaps "State of driver" would have been better. Hmm, re-labelling time I think.

You thinking of a speedo check at the critical moment by any chance? You're right though. It should be in there, but I'm not sure exactly how. I'm not keen on "luck" as it could arguably be applied to any of them. An oily road surface would be bad luck, but that's in the road condition box. I'd rather try to build the sort of thing you mention into one of the others, perhaps driver state again.

In my mind I had that off the chart, but failed to say so. To clarify, the chart is showing what's involved between the earliest opportunity to see a hazard and actually hitting it. Probably needs a rethink to make that obvious.

Not quite with you there. Can you explain a bit more?

In "Condition of road".

Also in "Condition of road" really, but these tow you've mentioned could be real biggies. That would mean I've underestimated the potential importance and perhaps stuck it in the wrong place. Hmmm, if they're there then "Condition of road" could well be more important than where I've put it, but if not then it might be right. I'm not sure how to show this. Probably not in a flow chart.

"Ding" moment! Like it. I think "Time hazard observed" fits this, though now I re-read it I see I've chosen the words poorly. It sounds like I'm saying amount of time spent looking at the hazard like a lemon wondering WTF to do and thinking "this is gonna hurt" and that's not at all what I meant. I think that's another label I need to change. Something along the lines of "exact moment of recognition of danger". "Ding" is a lot snappier though.

Well, it's very basic at this stage and like I said, I'm already unsure that a flow chart is the right kind of thing for this, at least when it comes to refining it. I've tried to keep it as simple as possible by including as many small factors under a sort of group heading, especially those relating to the car, the road and the driver. Trouble is that means that those now have potentially huge variability. A series of overlapping bars might be a better way. That would take care of having to make those fine judgements needed to get at the average rankings. Still, early days.

That was about as basic as it gets. Drawing toolbar in Excel, lose the gridlines, screencap, paste into PS and crop out the junk. Editing and redrafting would go the same way unless someone can suggest some clever bit of freeware/shareware. Meantime I'll have a play in PS to see if I can build on the bar thing. Make a change from propping one up.

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Make everything as simple as possible, but not simpler - Einstein

All interesting points noted. This one needs a reply:



Ok. In the first place there's a reason we're not starting off from 70mph in town. That reason is mainly drivers' perception of "regional" risk.

Secondly, in many situations where an accident takes place local conditions cause drivers to reduce speed. (Consider passing a school with kids spilling off the pavement - local risk makes us slow down irrespective of any individual hazard)

I think these inputs to pre-incident speed are crucial to road safety, and they are usually ignored - we shouldn't be making that mistake.

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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

I see what you're getting at now. On a motorway initial speed is higher simply because it's a motorway, and rush hour on the Strand it's pretty low just because it's rush hour on the Strand. So where a collision occurs can have a big effect on what the speed was to start with, which in turn... We could possibly include it in "Road condition" if we rearrange things to reflect that this may now affect initial speed. Not sure if the driver's perception of regional risk is part of that, or is something else for the "Driver factors" (or whatever we call it). It's kind of both. Obviously if the character of the road and immediate environment is such that the driver is fooled into setting an inappropriate speed it's not just a driver factor. In that case it's likely that the nature of the road and inexperience have both gone against him.
PS is no good for this. I need to start with a pencil again.

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Make everything as simple as possible, but not simpler - Einstein

Hi all, I'm back from holidays and just starting the l o n g task of catching up.

Throughout this discussion everything on focused on the driver and his/her vehicle. If the hazard is animal what about allowing for their reaction as well? Other than a suicide attempt this is a major component.

Pedestrian steps off curb, driver spots hazard and hits brakes and may have enough time to also hit the horn. Pedestrian hears noise and jumps back. Accident avoided or impact area reduced.

Steering does not appear to hold much weight in the debate either and yet is probably one of the most important tools for avoiding the hazard. Most modern cars have ABS and so an experienced driver will brake AND steer away from the hazard.

Given the choice of a parked car and a pedestrian I know which one I'd go for, whereas should the hazard be a dog or a cat I would choose the lessor impact of the animal.

Obviously none of these factors affect the "tree" example but IMO most crashes do have more options than to simply brake and steer straight ahead.

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Ross

Yes I'm a hoon, but only on the track!!!!

Hi Ross. I wondered where you'd got to.
All true, but if we're thinking about everthing that plays a role from a nanosecond after the point where physics makes a collision unavoidable, how much does steering or using the horn affect the outcome? Impact might be on another part of the car, I suppose, so it's possible to turn a head on or a T-bone into a side swipe. For some stationary objects, like trees and lamposts, it's probably better not to hit 'em sideways, so steering could change things there as well. Would either make a big difference if we're talking about pedestrians? If steering out a bit or the ped hearing the horn and jumping back not quite in time that might get them side swiped instead. I have no idea if that would be better or worse, but if it meant a broken leg rather than a pine box then it could be quite important. One for Mad Moggie and his doctor pals (who are sick, sick puppies BTW if that CD is anything to go by ), is getting hit in a different way a bigger element of survivability than speed?

If you're wondering why there's not much weight given to avoiding the hazard in this thread it might be due to one or two road safety ads here that focus on the message higher speed=bigger splat therefore slow down. One in aprticular deals with two situations: child hit at 40mph ends up dead against a tree, and when she's hit a 30mph she's injured in the road but alive. Download or watch it here (just over 3 megs) or read the blurb here. The implication is that once a collision cannot be avoided speed is the most important factor in determining how bad the crash is, and from that many people are going to think of speed beforehand rather than impact speed which is almost always going to be much lower. Even then, impact speed itself is changed by other factors - when are the brakes applied is very important, which in turn is strongly influenced by when the hazard is first seen, which in turn is affected by the state of the driver yadda, yadda, yadda. The ad ignores everything but impact speed, and even then fails to distinguish between that and free travelling speed just before the point of no return.

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Make everything as simple as possible, but not simpler - Einstein

I understand and have seen the commercial but the commercial is CRAP. We have similar commercials over here with a girl on a bike riding in front of a car but there is no attempt by the driver to avoid the collision, just a big screech and thump.

OK, basic drivers might freeze up and do that but what about showing that the steering is an option in the ad rather than try and make out that there is nothing else you can do? How about training drivers through these ads as well as showing the potential for disaster if the speed is truly excessive?

I have never seen an ad (other than from car manufacturers) that shows that steering is an option. I have never seen or heard of a driving test that incorporates an emergency brake and avoid situation.

There are almost always other options in an emergency than just the brake pedal so how about some education on that for a change?

Just back and already ranting...

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Ross

Yes I'm a hoon, but only on the track!!!!

Have not read through all this thread yet - but the general rule of thumb is that the average driver reacts to any hazard in 0.5 to 0.7 seconds. That is the length of time it takes for a brain to register and start feathering the brake. We all vary - but one second is far too long.

In that time we have probably travelled about say 7 metres if yuur reaction is 0.5 metres and you are travelling at 30 mph.

Of course, driver's health, distraction, luck, road conditions are all going to play a significant role in any accident. The contribution to severity of outcome is going to be linked to how hard the impact - weight of vehicle, speed of vehicle ... and so on.

One of the reasons why I am hammering the COAST message here. It is not a magic solution - but it helps us all choose the speed in which we can see to be clear to stop comfortably in.


My brother within GMP has told me about the inquest into a child's death today. Twelve years old and she stepped out from between parked cars into the path of a police car on a shout. All sirens and lights were flashing and the road was clear. He was travelling at 60 mph and there was literelly nothing he could do as she stepped out and literally walked in front of his car. I understand the colleague from Manchester has endured two years of torture reliving the scene in his mind.

Let's see if you hit a tree at speed of say 50 mph - in the first 2/10th seconds the bonnet will rise an crumple the wings will make contact with the tree causing further crumpling of the car. At the same time the driver will continue travelling forwards at the same speed as he was before impact. His legs would snap at this point. In the next tenth of a second his body is off the seat and his chest is meeting with the steering column. The front of the car is completely smashed by now - but the driver is still moving forwards and he gets impaled on the steering column as the rear of the car rises. The chassis then bends like cardboard and the shock kills. Of course - drivers such as these are usually young and there is also some other factor like drink ,drugs, showing off, joy riding in this type of incident.


I could give a very graphic account of other accidents I have investigated and the above scene would even fit what happened to Wildy's car - to certain extent. The difference being that she saw the danger and took some action to reduce the damage.

That's the severity if you hit something at speed, and asignificant number of accidents appear to occur if COAST is not present - or some other factor such as an impairment is evident - which cause slwo reaction and an inappropriate choice of speed, position and approach.

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A SMILE is a curve that sets everything straight (P Diller).

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Approach love and cooking with reckless abandon - but driving with a smile and a COAST calm mind.

Some of that makes grim reading IG, and I feel sorry for the GMP guy particularly. Just the thought of it...

IG can I ask you, when you guys investigate a crash is there normally an order of things you look for? Like check for driver impairment first, then check the vehicle for defects, then see what the speed was, then when braking began and so on. Or does the order depend on each situation and changes from one crash scene to another? Or on convenience (can't breathalyse the driver if he's surrounded by paramedics I imagine)?

_________________
Make everything as simple as possible, but not simpler - Einstein

Aye - nasty story for the GMP guy - and the little girl was by all accounts a pleasant child who made a tragic mistake. The cop made the statement himself - at the inquest - out of respect for the family and he broke down in tears. It's everyone's worst nightmare - the genuine "suddenly and from nowhere".


Yes - depends on type of accident. Witness statements are taken at the scene if possible. Or as soon as possible at the hospital.

Yes - we close off the area, look for evidence on the road - oil, grease, potholes. The car's position is photographed and in situ forensic tests are taken before we send it to the garage to be fully examined for defects. Tyres, brakes, engine - all looked at to try to establish if there was a defect and how far it contributed to a KSI.

We wait until the doctor's have treated before we interview if person is medium/seriously injured. Slight injuries - we usually take statements as sson as - but have to tak account of shock as well. We usually arrange a second interview to clarify initial statements. This is to estbalish speed, position, other factors and witness statements do vary as well. We try to get the first impression view and then clarify in a later interview. We then view the statements objectively and view alongside all other information such as impact, injury, car defects (if any) and we also look at driving histories.

Lot of other factors are alos looked at as wel - but these are the initial ones.

Breath tests - S9 of RTA 1988 applies - the doctor in charge of treatment has to be notified - and he can refuse to allow it if it interferes with the treatment. If test can be made - two doctors must agree to do it: one taking the test and the one in charge of the treatment (under S7)

_________________
Take with a chuckle or a grain of salt
Drive without COAST and it's all your own fault!

A SMILE is a curve that sets everything straight (P Diller).

A Smiley Per post
FINES USfor our COAST!

Approach love and cooking with reckless abandon - but driving with a smile and a COAST calm mind.

But it wasn't "suddenly and from nowhere", was it? To my mind, the driver made a serious error and that compounded the girl's error and resulted in her death. If he hadn't been on a shout, or if it had been any other driver, I'd imagine there would have been a charge of causing death by dangerous driving. The fact he was on a shout mitigates the error but does not eliminate it.

It's easy to be wise with hindsight and I don't believe the officer involved deserves additional punishment, but the fact of the parked cars makes this speed inappropriate, even 'on a shout', unless (possibly) it was possible to position the vehicle sufficiently wide of the parked cars to allow an emerging pedestrian to see and avoid or be seen and avoided.

I would imagine that this tragic incident comes into your mind whenever you have to switch on blues and twos in similar circumstances?

The full story was in "Manchester Evening News!" Police were on their way to a violent fight involving weapons. Witness (car mechanic) saw a marked Volvo - sirens and lights - rush past. He pulled out into the junction and noted a police van - also displaying sirens and lights closing in on him. He pulled in - shortly before a pelican crossing. The van passed him at about 60 mph.

Forty feet after the pelican crossing he saw the girl at the same time the police driver would have seen her - step oput. It was very quick and he had no time to avoid or hit the brakes - according to the witness per the newspaper report.

Yhe twleve year old had been a youth club and her mother usually picks her up. On this occasion she decided not to wait.

Staff at the youth club siad she was on a high that evening and had boasted that she had drunk 4 cans of strong lager - allegedly given to her by a 17 year old. A volunteer offered to walk her home - and he said the girl just veered intothe road without looking and very suddenly - and was struck by the police van.

She was tossed into the air in the impact and the police driver stopped and tried to give first aid on the spot. Howver, she died 4 days later in Manchester Children's ICU

Apparently the volunteer had taken her home - but found her mother had set off to meet her and they had missed each other on the way. It was when they were rtracing their steps that the girl rushed into the roadway.

It is still a very sad story - and no guarantee she would have lived had he been driving at 30 mph or less given this is a police van.

Feel sorry for the girl's family and the police officer. Could happen to anyone.

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