Causation
312There remains a question as to whether the failures of the Council, (a) to restrict the speed limit to 60km/h and (b) to include a slippery road sign, caused the accident. The question of causation turned on three issues, namely, (a) the speed at which the deceased was driving when she reached the first section of resurfaced road; (b) the point at which she lost control of the vehicle, and (c) the likely effect of a restricted speed zone and a slippery road sign.
313For reasons which will be explained, the experts were in agreement that the deceased was travelling in excess of 80km/h when she lost control. Mr Johnston undertook a calculation, working back from the point of impact, to suggest an initial speed of about 67km/h-80km/h (first report, par 9.33), which he described as "very approximate and most probably a conservative estimate", expressing a "realistic estimate" as between 80km/h and 100km/h. Mr Stuart-Smith calculated a speed of 88km/h "just before she commenced her oversteer", also expressing the view that the figure may have been higher: report, p 36.
314The section of roadway on which the deceased lost control included three areas of resurfacing. The distances were revealed in the following extract from the trial judge's summary of the facts, taken from her reasons for a ruling on evidence, John Curtis v Harden Shire Council [2012] NSWSC 84:
"[8] The tree Ms Paterson struck was in alignment with the commencement of the third section of resealed road (in a southbound direction). This was approximately 210m from where the first section of resealing commenced. There were distinct tyre marks curving across the centre line from left to right on the immediately preceding unworked second section. The tyre marks commenced about 45m from the point of impact. It is common ground that the appearance of the marks and their arrangement are consistent with her vehicle being in a distinct yaw as it 'side slipped' and then rotated in a 180 degree arc towards the point of impact.
[9] The first section of reseal travelling north extended over 89m and commenced part of the distance around a 230m curve in the roadway to the right. The second section of reseal over which Ms Paterson must also have passed before losing control ... measured 31m with an unworked 40m section of road intervening between those two segments. There were vehicle track marks of differing density and orientation over both the first and second resealed sections. There were no tyre marks or tracks of any kind on the unworked section in between those two sections."
315Thus, in the southbound direction in which the deceased was travelling, the road commenced a gently curve to the right, followed by a curve back to the left, the latter being beyond the point of impact. The first resealed section (with loose aggregate) commenced as the road eased out of the right hand curve. The resealed section was 87m long, and was followed by a gap of 39m before the second section of resealed road commenced. At least from a point halfway through the first resealed section to the point of impact, the road was straight.
316The tyre marks on the road which were associated with the deceased's vehicle commenced after she had covered approximately 150m from the beginning of the first resealed section. The first tyre mark indicated that as she was coming out of the second resealed area she was on the wrong side of the road, but directing her vehicle back towards the correct side of the road. Immediately she left the second resealed surface, some 54m before the point of impact, there were no tyre marks, however it was thereafter possible to chart her position as she crossed back to the correct side of the road at the gap between the second and third resealed surfaces (an area where there was no loose aggregate) but immediately overcorrected, so that she lost control of the vehicle some 45m before the point of impact with the tree, which was on the right hand (wrong) side of the road, with the rear of the car apparently "fishtailing" so that by the time she left the road on the wrong side and struck the tree, the car had swung through approximately 120 degrees. (By the time it came to rest behind the tree, it had completed a 180 degree turn.)
317The trial judge described the manner in which the question of causation was addressed by the parties in the following passage:
"[81] In the way the plaintiffs' case on liability was advanced at trial ... it was conceded that the patent evidence of Ms Paterson's yawing out of control 45 metres from the point of impact (160 metres from the commencement of the roadworks), associated with some evidence of a loss of control in the preceding resurfaced second section by reference to the faint mark in the gravel on the incorrect side of the road, would not support a finding of factual causation. It was common ground that the plaintiffs' case depended upon my being satisfied that Ms Paterson probably lost control in the first resurfaced section on encountering the loose gravel while travelling at or near 100 km/h, and that it was this that caused her to veer progressively off to the right before she travelled (probably on the incorrect side of the road) for some distance, before returning to the correct side of the road after her failed efforts to regain control ...."
318After considering in fine detail the competing hypotheses presented by the experts on the question of causation, the trial judge concluded at [113]:
"Given the way the plaintiffs have put their case, the failure to persuade me that control was probably lost because of a loss of traction at the beginning of the first resurfaced section, a primary fact upon which the further and critical finding of factual causation depends, carries with it the consequence that I am not persuaded that but for the failure to provide for and position appropriate signage the accident would not have occurred."
319The appellants' case before this Court implicitly, and somewhat obliquely (there being no ground of appeal specifically addressing this question) took issue with the underlying approach of the trial judge. Secondly, it took issue with the actual conclusion with respect to lack of satisfaction as to any loss of control upon entering the first resurfaced area. Thirdly, the grounds of appeal asserted that the trial judge erred in not finding that causation had been proved pursuant to s 5D(2) of the Civil Liability Act, whilst conceding that the point had not been argued before her. Nothing was said, either in written submissions or in oral argument, in support of this third approach: the ground should be taken to have been abandoned. It remains necessary to consider whether causation was established pursuant to s 5D(1) of the Civil Liability Act. It is convenient to set out the whole section.
5D General principles
(1) A determination that negligence caused particular harm comprises the following elements:
(a) that the negligence was a necessary condition of the occurrence of the harm (factual causation), and
(b) that it is appropriate for the scope of the negligent person's liability to extend to the harm so caused (scope of liability).
(2) In determining in an exceptional case, in accordance with established principles, whether negligence that cannot be established as a necessary condition of the occurrence of harm should be accepted as establishing factual causation, the court is to consider (amongst other relevant things) whether or not and why responsibility for the harm should be imposed on the negligent party.
(3) If it is relevant to the determination of factual causation to determine what the person who suffered harm would have done if the negligent person had not been negligent:
(a) the matter is to be determined subjectively in the light of all relevant circumstances, subject to paragraph (b), and
(b) any statement made by the person after suffering the harm about what he or she would have done is inadmissible except to the extent (if any) that the statement is against his or her interest.
(4) For the purpose of determining the scope of liability, the court is to consider (amongst other relevant things) whether or not and why responsibility for the harm should be imposed on the negligent party.
320The plaintiffs bore the onus of proving on the balance of probabilities "any fact relevant to the issue of causation": s 5E. Although the section does not say so in so many words, it should be accepted that the plaintiffs bore the onus of proving the ultimate factual inference of causation. The appellants contended that this was not inconsistent with "probabilistic reasoning", by which they meant being satisfied of an inference on the balance of probabilities even where there were competing inferences, so long as the one relied upon was more probable than the others.
321One purpose of s 5D(1), dividing causation into two elements, is to encourage a degree of precision in the way in which such issues are presented and determined. In warning cases (of which this is one) particular complexities can arise. For example, as the trial judge noted with deliberate care, the manner in which the case was argued before her depended upon the plaintiffs establishing that there was loss of control upon reaching the first unsealed section. That was not necessarily how a methodical application of s 5D(1) would operate. The necessary connection to be established was between (a) the failure to warn of the slippery surface of the roadway and to impose a speed restriction because of the slippery surface and (b) the injury resulting from loss of control.
322The evidence did not clearly demonstrate that the deceased's loss of control resulted from the slippery surface or excessive speed. However, whatever the cause, it was common ground between the experts that, had she been travelling at 60km/h she would have stood a much better chance of regaining control, assuming that she had lost it, for whatever reason. On that approach, it was not necessary to establish that she lost control because of the slippery surface in negotiating the resealed sections. Arguably, the harm would not have occurred if the speed limit had been imposed and, thus, one element of the negligence (the absence of a speed restriction) was at least a sufficient condition for the harm.
323A similar (though by no means identical) issue arose in Wallace v Kam [2013] HCA 19; 250 CLR 375, as discussed in the joint reasons of French CJ, Crennan, Kiefel, Gageler and Keane JJ. The plaintiff underwent a surgical procedure which was accompanied by two significant inherent risks of which he was not warned. The trial judge (Harrison J) held that if warned of the risk which materialised, he would nevertheless have undergone the procedure. He therefore dismissed the claim. On appeal to this Court, the plaintiff alleged that if warned of the other (more serious) risk, he would have declined the operation. This Court accepted that factual premise, but concluded that he was not entitled to recover. The case turned on the application of s 5D of the Civil Liability Act. The High Court upheld that result. Referring to the analysis earlier undertaken in Strong v Woolworths Ltd [2012] HCA 5; 246 CLR 182 at [18], the joint reasons in Wallace v Kam noted at [16]:
"The determination of factual causation in accordance with s 5D(1)(a) involves nothing more or less than the application of a 'but for' test of causation. That is to say, a determination in accordance with s 5D(1)(a) that negligence was a necessary condition of the occurrence of harm is nothing more or less than a determination on the balance of probabilities that the harm that in fact occurred would not have occurred absent the negligence."
324The joint reasons continued at [19]:
"Another scenario is where the patient would have chosen not to undergo the treatment at all if warned of all material risks. In that scenario, a determination of factual causation can be made without difficulty. That is because, absent the negligent failure to warn, the treatment would not have gone ahead at any time and the physical injury would not have been sustained."
325It is at this point that the analogy arises in the present case. Although there are factual findings to be identified, it may be assumed for present purposes that, (a) in veering to the wrong side of the road and attempting to correct her position unsuccessfully, the slippery surface caused by the loose aggregate played no part; (b) had there been a sign showing a restricted speed limit of 60km/h, the deceased would have complied with it, and (c) had she veered onto the wrong side of the road, she would nevertheless have been able to correct her position without losing control of the vehicle. The harm would therefore not have occurred. In these circumstances, should the Council be liable?
326The purpose of the restricted speed zone was to prevent loss of control on the resealed sections, not to limit the consequences of veering across the road through sleepiness or inattention. This, as the High Court noted in Wallace v Kam at [22]-[23], requires a finding as to the "scope of liability" in accordance with s 5D(1)(b) and, to the extent that it is a novel case, by application of s 5D(4). As the joint reasons in Wallace v Kam further explained, attribution of responsibility requires consideration of the purpose served by the imposition of the particular duty of care which has been breached. In some circumstances, liability has been excluded where the harm which results may be described as "sheer coincidence": Chester v Afshar [2005] 1 AC 134 at [94] (Lord Walker of Gestingthorpe). Lord Walker gave the example of a taxi driver driving too fast, with the result that the cab was in the way of a falling tree and the passenger was injured. Absent breach of the duty to drive slower, the injury would not have occurred; nevertheless liability should not attach. The example is similar to that referred to in Wallace v Kam, "of a mountaineer who is negligently advised by a doctor that his knee is fit to make a difficult climb and who then makes the climb, which he would not have made if properly advised about his knee, only to be injured in an avalanche": at [24]. In the language of Lord Hoffmann in Banque Bruxelles Lambert SA v Eagle Star Insurance Co Ltd [1997] AC 191 at 213, the injury was "a foreseeable consequence of mountaineering but has nothing to do with his knee".
327The present case is distinguishable from Wallace v Kam in two important respects (amongst others). First, the nature of the harm suffered by the plaintiff in Wallace v Kam was different in kind, resulting from the materialisation of a risk, different from that which he would not have accepted. In the present case, the harm (losing control of the vehicle and sliding off the road) is of the same kind as that which would have resulted had control been lost due to skidding on loose aggregate. On the other hand, in Wallace v Kam both risks were risks of which the plaintiff should have been warned. In the present case, the risk which eventuated (on the assumptions identified above) was the risk of leaving the road through inattention or distraction, being a risk of which the Council had no duty to warn or guard against by reducing the speed limit.
328In the present case, and on the assumptions set out above, the liability of the Council should not extend to the harm suffered, if the harm did not result from the slippery nature of the loose aggregate. On those assumptions, it was in the nature of a coincidence that her inattention occurred at a point where she should have been warned to slow down because of a risk which she (and no doubt many others) had successfully negotiated.
329Although the foregoing analysis was not undertaken by the trial judge, that was because its conclusion was accepted by the plaintiffs without demur. Accordingly, to the extent that the appellants relied in their written submissions in this Court (at paragraph 26) on the fact that, if the deceased had been travelling at 60km/h she would have been able to respond better to her loss of control, as an independent basis of asserting liability, that should not be accepted.
330The remaining question is whether the appellants' submissions that the trial judge should have been satisfied that the loose aggregate was a material contributor to the loss of control, should be accepted.
331The appellants contended that, where the precise cause of the accident was unknown, the driver being deceased and there being no eyewitnesses, the trial judge was required to determine whether the negligence of the respondent was "a necessary condition of the appellants' harm by the process of probabilistic reasoning adopted in Shoeys Pty Ltd v Allan" [1991] Aust Torts Rep ¶81-104, relied on in Woolworths Ltd v Strong [2010] NSWCA 282 at [60] and referred to without dissent by the High Court in Strong v Woolworths Ltd at [30]. That premise may be accepted: the proposition that the trial judge did not in fact adopt such an approach should be rejected.
332The trial judge noted that the question of causation was to be determined in accordance with s 5D of the Civil Liability Act, and that the burden of proof lay on the plaintiffs, pursuant to s 5E: at [85]. She further noted the acceptance by Ipp JA in Sydney South West Area Health Service v Stamoulis [2009] NSWCA 153 at [138] that a finding of causation "may be made even when the expert evidence does not rise above the possible; the question is always whether the evidence as a whole establishes causation on a balance of probabilities": set out at [84]. In addition, the trial judge referred to the principles stated by McDougall J in this Court, (McColl and Bell JJA agreeing) in Nguyen v Cosmopolitan Homes [2008] NSWCA 246 at [44]-[45]. McDougall J noted that "an actual persuasion" was required to satisfy the burden of proof, meaning that the court must be satisfied that "the probabilities of the fact's existence are greater than the possibilities of its non-existence": at [55].
333The comparison of probabilities with possibilities, the former satisfying the standard of proof while the latter do not, as used by Ipp JA and McDougall J, is entirely conventional. In one sense, any competing finding may be described as a possibility and the likelihood of its occurrence as a probability; in this context, however, it is common to use the term "probability" to refer to a state of satisfaction greater than 50% and the term "possibility" to refer to something less likely. In any event, such linguistic usage could not demonstrate error.
334It is true that McDougall J referred in Nguyen at [44] to Dixon J in Briginshaw v Briginshaw [1938] HCA 34; 60 CLR 336. However, Briginshaw stands for more than a single proposition. The proposition relied on by McDougall J was expressly identified by him as that set out by Dixon, Evatt and McTiernan JJ in Helton v Allen [1940] HCA 20; 63 CLR 691 at 712:
"'When the law requires the proof of any fact, the tribunal must feel an actual persuasion of its occurrence or existence before it can be found. It cannot be found as a result of a mere mechanical comparison of probabilities independently of any belief in its reality'."
335This straightforward proposition, applied daily by judges in civil cases, was not misunderstood by this Court in Nguyen, nor is there any reason to suppose that the trial judge misapprehended its meaning in this case.
336The evidence relied on by the parties fell into three categories. First, there were the objective features of the environment in which the accident occurred, including the signs, the resealed sections of the road with loose aggregate, the unaltered sections and the general topography. Secondly, there was the evidence which sought to reconstruct the events immediately preceding the impact of the car with the tree after it left the roadway. This evidence was primarily the analysis by the expert engineers, based on notes and photographs taken by two Council engineers (Messrs Ellis and Crisp) and the police officers (Messrs Hando and Brand) who attended the scene and recorded their observations. The engineers also made their own observations of the scene of the accident, although much later.
337Thirdly, there was an assortment of material from which less direct inferences could be drawn as to the probabilities of various events. This evidence included the circumstances in which another driver, Ms Skorulis, travelling in the opposite direction, had lost control some 12 hours earlier in the same area. It also included the character and driving history of the deceased, namely that she had an "unblemished driving record over 20 years" and had not been involved in previous accidents, together with the absence of any evidence that her capacity to drive on the day of the accident was impaired in any way.
338The only significant evidence given orally in relation to this issue was that of the two engineering experts. The appellants noted that Mr Stuart-Smith, called by the respondent, had been the subject of "pointed questions" by the trial judge, the passage in the transcript being that set out above at [299]. The submissions on appeal stated:
"At the very least, the exchanges between her Honour and the Respondent's expert illustrate that his evidence was presented from a partisan perspective. Where it conflicted with that of the Appellants' expert, it ought to have been entirely rejected."
339This submission should not be accepted. First, the passage set out above in which the trial judge pressed Mr Stuart-Smith to consider whether his adherence to his written report was credible related specifically to the need for a restricted speed limit and a warning sign. It had nothing to do with the issue of causation. Secondly, the trial judge made no finding adverse to the reliability of Mr Stuart-Smith's testimony, either in respect of this issue, or more generally. Given that the issue had been raised specifically by the judge, this cannot have been an oversight. Thirdly, even bearing this robust exchange in mind, there is no hint in Mr Stuart-Smith's evidence with respect to causation that his opinions did not comply with the obligations of an expert witness, with which he said he was familiar.
340In oral submissions, the appellants focused on two specific passages in the reasoning of the trial judge with respect to causation which were said to reveal error. The first, at [77], was in the following terms:
"It was agreed between the experts that there was no physical evidence which was capable of fixing where Ms Paterson was likely to have first lost control of her vehicle over that 210 metres."
341The distance of 210m was calculated from the commencement of the first resurfaced section to the point of impact. The trial judge also noted (again as a matter of agreement) that, according to the physical evidence, the vehicle was under control when the deceased entered upon the first resurfaced section. Importantly, neither expert viewed the physical evidence in situ: Mr Johnston was not engaged by the plaintiffs until more than three years after the accident. The road surface was swept clear of gravel later on the afternoon of the accident: at [78]. Accordingly, both experts were dependent upon the sketches and photographs taken by police and Council officers on the day of the accident.
342Mr Crisp, the Council's engineering assistant at the time of the accident, prepared a sketch diagram which included tyre marks running the length of the first resealed section (some 87m) which commenced with the vehicle in its correct lane and left at the southern end of the resealed section with the nearside tyre mark approximately at the centre lane of the road (meaning that the vehicle was almost entirely on the wrong side of the road and continuing in that direction). Senior Constable Hando, who attended the scene and prepared the primary police account of the events stated, in relation to the first resealed section (which he measured with precision) that "[t]here were no visible marks on the road surface." He took a number of photographs of the roadway.
343In his initial written report, Mr Johnston stated:
"9.46 As there were no witnesses to the actual loss of control event, the fact that Ms Curtis did not survive to provide an account and the limited quality of post incident recording of the forensic evidence it is necessary to hypothesise on the probable loss of control mechanism.
9.47 It is certainly suggested by all descriptions of the tyremarks that this event is initiated by a loss of traction."
344In his written report, Mr Stuart-Smith stated at 12.2:
"As was stated by Senior Constable Brand, there is no apparent reason for the Deceased having drifted or steered to the right side of the road. There is no evidence in the photographs of slideslip marks in the loose material in either of the two resealed surfaces traversed by the Deceased up to the point where she approached the right side of the road where the preliminary tyre mark was reported to have been located."
345In the joint expert report, the engineers were asked:
"What was the path taken by the deceased's vehicle from the curve at the start of the roadworks to the point at which the vehicle came to rest? Please list the physical and other evidence which supports the conclusion as to the path taken."
346The agreed answer commenced:
"The vehicle appears to have deviated from the left side of the road within the first patch to the right side of the road at the end of the second patch.
The evidence for this is a possible/probable (RSS/GJ) tyre mark shown in some diagrams and possibly evident in a Council photograph."
347The latter sentence indicates that Mr Stuart-Smith thought that the tyre mark indicated in diagrams was only possibly a tyre mark, whereas Mr Johnston thought it was indicated as being probably a tyre mark, although both agreed that it was only "possibly evident" in a Council photograph. There is no suggestion that it was evident in any of the photographs taken by the police officer.
348The engineers were then asked, "What is the earliest evidence of the deceased losing control? What and where is that evidence?" Mr Stuart-Smith expressed the view that "[t]he earliest clear evidence of loss of control is at the start of the tyre marks located about 45 metres before the [point of impact]." In his view:
"There is no evidence of loss of control at the curve overlapping the first patch", as suggested by Mr Johnston. The factors identified by Mr Johnston are not evidence."
349Mr Johnston expressed the view that the driver had "commenced to lose control around the start of the first section of reseal within the first horizontal curve." He described the evidence as being "the contemporaneous diagrams by a Council officer, the possible indication of a tyre mark within the Council photographs and the known passage of the vehicle from the left side of the road to the right side of the road". The trial judge was entitled to take the view adopted by Mr Stuart-Smith that this material was not "physical evidence" of a loss of control in the first section of resealed surface. That view was not shown to be wrong.
350The experts were asked a further question: "What does the evidence say was the most likely cause of the loss of control...?" Mr Johnston's view was recorded as being "that initial loss of control was probably due to a partial loss of traction upon transitioning into the first section of reseal. This has caused increased clockwise slip angle and a resulting deviation of the vehicle path to the right." Mr Stuart-Smith repeated his view that there was no loss of control at the curve overlapping the first patch and continued:
"Had the vehicle lost control in loose gravel, evidence, such as tyre marks and windrows on the loose material of the first patch would have been present. No such evidence was recorded by Police or can be seen in photographs.
Mr Johnston's suggestion that the vehicle lost control as a result of rounding the curve in loose gravel is not supported by evidence where evidence would have been expected."
351Mr Johnston did not identify any other evidence for the proposed loss of control in the first section, merely referring back to that which had been identified before. If that did not constitute "physical evidence", none was added.
352In the course of oral evidence, Mr Johnston expressed the view that because the "potential effect of the loose gravel" was to reduce traction, that was the "precipitating factor": Tcpt, p 204(35). He then explained (Tcpt, 205(30)):
"If she lost traction on that corner, would you expect an initiation of a clock-wise rotation of the vehicle, or a sense of clock-wise rotation of the vehicle, yes."
353The questioning continued by Mr Sheldon (for the Council):
"SHELDON: If you consider that Ms [Paterson] lost control with a clock-wise rotation of the vehicle, you would not expect to see a straight line across to the opposite side of the road as a result of that loss of control, would you?
WITNESS JOHNSTON: Not where that actually occurred. Later on, if that was the path the vehicle took, you might. But where the initial precipitating event was, no, you I would not expect a line there.
SHELDON: But if that is the path the vehicle took later on, wouldn't you have to assume the regaining by the driver of complete control of the vehicle in the absence of marks, indicating that the vehicle was in a yaw, as to [come] down the incorrect side of the road?
WITNESS JOHNSTON: Certainly not complete control, but I would expect the vehicle was under control and largely corrected. So, it was now heading in the wrong direction, but was no longer continuing to rotate.
SHELDON: Would you expect there to be marks on the road showing the loss of control that precipitated that manoeuvre?
WITNESS JOHNSTON: Provided the area was not completely contaminated by material, yes. I would expect somewhere up near where the police car is, a trained eye would see, or find, that evidence, potentially.
HER HONOUR: A trained eye would find what?
WITNESS JOHNSTON: A trained eye would find some evidence of that type of loss of control. By that I don't mean general duties police officers or crime scene officers.
HER HONOUR: When you say that loss of control --
WITNESS JOHNSTON: A clock-wise rotation of the vehicles due to traction. I suggest if Mr Stuart-Smith or I, if we investigated, might find it.
SHELDON: When you say might find it, that is in the realms of speculation --
...
WITNESS JOHNSON: I said that subject to a lot of contamination being up there. So, if we got there fresh, and no one else had been on the roadway and it was clear, I would be fairly confident we would pick it up....
SHELDON: As far as that view applies to this case, that is mere speculation, isn't it?
WITNESS JOHNSTON: That's right, we can't even look at a photograph of that area and tell you it's there. There's just not even a photograph there of that."
354The first passage in the judgment of the trial judge subject to challenge (that there was no physical evidence which was capable of fixing where Ms Paterson was likely to have first lost control of her vehicle) was intended to refer to the question whether there was evidence of any loss of control in the first resealed section. The statement is clearly correct: the submissions to the contrary must be rejected.
355The second challenge came to a passage at [83]:
"Although Mr Stuart-Smith conceded that it was possible that control was lost in the first resurfaced section, the absence of physical evidence showing the vehicle's passage from the correct to the incorrect side of the road under a loss of traction on the curve - evidence which he expected would have been clearly visible on the road surface were that to have occurred - did not allow him to conclude that the loss of control was probably due to a loss of available friction when, in his view, other competing hypotheses were open, including momentary inattention, drowsiness or fatigue."
356The trial judge continued, in a passage central to her conclusion:
"[99] Accepting that the light tyre marks observed by Mr Ellis, and shown in photographs 19 and 20, were probably deposited by Ms Paterson's vehicle, Mr Stuart-Smith noted that she deviated from left to right over the first section of resurfaced roadway in a reasonably straight line without any obvious attempt to correct that course. The photographs objectively support that description. In his view, this was inconsistent with a driver experiencing a loss of traction or recovering or attempting to recover from a loss of traction.
[100] He also placed considerable reliance on the absence of any physical evidence indicating the tyres were rotating in a clockwise yaw or sideslip, which might have suggested that the precipitating cause of the deviation to the incorrect side of the road was a result of a loss of traction upon encountering the gravel surface as Ms Paterson continued to negotiate the moderate curve to the right. With no photograph of the road surface where the roadworks commenced or within metres of it (and where, on the plaintiffs' case, traction was lost) and no physical evidence on the road surface of any attempt by Ms Paterson to correct any sideslip or undertake any corrective manoeuvres noted either by the police, Mr Ellis or Mr [Crisp], evidence which Mr Stuart-Smith expected would be visible even to an untrained eye, it was his view that it was unlikely that control was lost as a result of a loss of traction upon encountering the gravel at the commencement of the roadworks. He was of the opinion that the probabilities favoured Ms Paterson deviating from her path around the curve in the first resurfaced section for a reason or reasons unconnected with encountering the gravel at an unsafe speed. While he appointed other hypotheses, including drowsiness or inattention, he was not invited to address whether such physical evidence as was apparent at the accident site supported either hypothesis."
357Although the appellants did not challenge the reasoning in [99], they did assert that the trial judge confused "loss of control" and "loss of traction". For this purpose, they relied upon a passage in the reasoning at [108] (italicised below), but in order to understand the particular passage, it is necessary to put it in its context, commencing at [107].
"[107] It is clear from this evidence that Mr Johnston's opinion was also informed by his belief (or expectation) that physical evidence on the road surface in the first section where he believed traction was lost would likely have been discernable to 'a trained eye', and that neither officers Brand and Hando nor Messrs Ellis and [Crisp] were sufficiently qualified to discern what Mr Johnston claimed he and Mr Stuart-Smith would have been able to discern and [identify] as a tyre mark of a vehicle in a clockwise yaw.
[108] Mr Johnston's assumption that the tyre marks were present but not seen could only support a finding that they were probably there if there were some evidence that the marks were there to be seen but overlooked. The obvious flaw in his reasoning is that if there were evidence of a yaw mark or sideslip proximate to where Ms Paterson entered the first resurfaced section (whether or not she regained control of the vehicle thereafter) there would be no need to proceed on the assumption that it was overlooked. To the extent that Mr Johnston's opinion that the probable cause of the accident was a loss of control in the first resurfaced section due to a loss of traction is based on the assumption that there either was physical evidence which was missed by all observers, or there might have been evidence that was missed by those people, the reasoning suffers from circularity in the sense that it is assumed that there were marks on the road because one would expect them to be present if there was a loss of control due to lack of traction. I am not persuaded that the theoretical possibility that the tyre marks were missed by those at the scene (and, in the case of Sergeant Brand, missed despite the fact that he was specifically looking for some evidence of the loss of control) permits an inference to be drawn that the tyre marks were there but missed."
358Referring to the italicised passage, as an example of the confusion, counsel's submissions proceeded (CA Tcpt, p 34(38)):
"Firstly, that passage ... involves a misconception that there would have to be a yaw or side-slipping mark for the vehicle to have lost control in the first section when it entered. That ignores Mr Johnson's evidence that a loss of control may be something less than a loss of traction. It is not the same as. The second error apparent in that paragraph is that Mr Johnson's opinion was based upon a loss of traction. It was never suggested that there was a loss of traction per se. What was suggested was loss of control occurred in the first section evident by those marks that Crisp and Ellis saw and which accounted for the crossing from the correct to the incorrect side of the road in circumstances where you would not expect it to have occurred."
359The criticism is obscure. As appears from the passage set out above at [343], from his first report, Mr Johnston was at pains to explain that the "mechanism" by which control was lost was a loss of traction on entering the first resurfaced section. From the appellants' perspective, there was a good reason to maintain such a position. If loss of traction did not lead to a loss of control, causing the vehicle to veer across the road, then the veering was to be accounted for by some other mechanism which was independent of the negligence of the respondent. Furthermore, "loss of traction" is a relative concept: it may or may not lead to a loss of control which causes the vehicle to go in an unintended direction. The appellants' case required that the loss of traction had that consequence. For the trial judge to refer to "a loss of control in the first resurfaced section due to a loss of traction" was to identify precisely what Mr Johnston hypothesised: it was the appellants' case.
360The trial judge considered that Mr Johnston's position was, if not circular, at least compromised. Mr Stuart-Smith's evidence, set out by the trial judge at [101], included the following proposition:
"So looking at the photograph, that's on the right-hand side of the photograph, in other words, Ms Paterson's left as she's coming towards us, so one would have expected some windrow or some build up of material, or some ... shading of the tyre mark to indicate some lateral displacement. But not only that. A vehicle doesn't just sideslip ... and then continue just travelling in that same sort of general direction. Once it starts to sideslip, it continues to rotate until the steering has twisted in the other direction, in which case, you either correct - control is regained or else you end up with an oversteer, and the mark is too long."
361Although, as the trial judge noted, Mr Johnston disagreed that "definite windrows or furrows would be expected to be created (or visible) under lateral displacement" - at [105] - she also accepted that it was his opinion that physical evidence would have been available "to a trained eye": at [107]. That approach was entirely consistent with the evidence set out above at [351]. In other words, Mr Johnston's hypothesis depended upon there being some physical evidence which had not been detected. Her Honour concluded that it remained just that: an hypothesis, which she could not be satisfied was probable rather than possible.
362There is nothing in that reasoning which gives rise to doubt: indeed, a careful consideration of the evidence and the manner in which the trial judge dealt with it leads me to the same conclusion.
363The thrust of the appellants' remaining submissions was that had proper weight been given to the circumstances in which another driver, Ms Skorulis, also lost control and went off the road, and had proper weight been given to the known characteristics of the deceased as a driver, it was more probable than not that the reduced traction on the first resealed section which led to her losing control of her vehicle.
364The submissions are unpersuasive. Although at times counsel sought to contend that the trial judge had ignored or not taken account of aspects of the evidence, her consideration of the relevant material was comprehensive. The real force of her rejection of the significance of Ms Skorulis' accident was that Mr Johnston had placed significant weight on aspects which he found compelling, as supportive of his conclusions as to how Ms Paterson lost control. However, Ms Skorulis had been travelling in the opposite direction, at midnight, and lost control on a different section of the road. The trial judge noted, at [112], "that Ms Skorulis' evidence and the objective facts bearing upon her accident, were capable of informing in a rational way how and why it was that Ms Paterson was on the incorrect side of the road some 150 metres from the commencement of roadwork". The trial judge continued:
"While I accept that there are a constellation of objective features in both accidents that Mr Johnston found compelling, and which prima facie would tend to suggest the accidents shared a common cause, to make the finding that they were both probably the result of encountering the gravel without adequate forewarning and under speed would also require me to be able to comfortably draw the inference (as distinct from simply assuming) that Ms Paterson, being a more experienced driver than Ms Skorulis, had managed to regain some control of her vehicle after a loss of traction (thus explaining the distance of 150 metres or more over which her vehicle travelled before control was ultimately lost) but Ms Skorulis did not. I am unable to draw that inference. Moreover, it was only after the experts gave further evidence that the marked dissimilarities between the known passage of Ms Skorulis' vehicle and the reconstructed passage of Ms Paterson's vehicle were highlighted."
365Ms Skorulis' accident in effect demonstrated that part of the appellants' case which was upheld, namely the need for speed restrictions and warnings as to the slippery surface. When one reaches the issue of causation, the risk is not in doubt: that the evidence establishes that another driver succumbed to the risk is of little significance in establishing how the deceased lost control. The trial judge was correct to focus on the evidence relating to the passage of the deceased's vehicle.
366So far as Ms Paterson's characteristics were concerned, there is nothing suggestive of error in the trial judge's analysis. It took into account and gave weight to the evidence of Ms Paterson's experience and carefulness as a driver. How much weight was given to her "unblemished" record was a matter for the trial judge. Even experienced drivers with good records are capable of momentary inadvertence; further, the evidence that she reached the resurfacing roadworks maintaining a speed of 100km/h, despite the 'roadworks ahead' and 'loose stones' signs required some allowance to be made for error of judgment. The trial judge had referred to the fact that it was "common ground that Ms Paterson was a careful and experienced driver who was familiar with the road": at [2]. It was referred to again in the passage at [112] set out above.