R v Bjordal - [2005] SASC 422

SUPREME COURT OF SOUTH AUSTRALIA
(Court of Criminal Appeal)
R v BJORDAL
Judgment of The Court of Criminal Appeal
(The Honourable Justice Debelle, The Honourable Justice Besanko and The Honourable Justice Vanstone)
10 November 2005
EVIDENCE - ADMISSIBILITY AND RELEVANCY - OPINION EVIDENCE - EXPERT OPINION - MOTOR VEHICLES
Appeal against conviction for death by dangerous driving – at trial evidence given by police officer as to likely speed of appellant’s vehicle – evidence based on formula – formula adjusted by officer to account for partially gravelled road surface – whether evidence based on adjusted formula admissible – whether officer had sufficient expertise to adjust formula – held, such evidence inadmissible as it did not constitute expert evidence – officer did not have sufficient expertise – appeal allowed, retrial ordered.
Makita (Australia) Pty Ltd v Sprowles (2001) 52 NSWLR 705, applied.
R v Clarke (2003) 87 SASR 203, distinguished.
Domican v The Queen (1992) 173 CLR 555; R v Bonython (1984) 38 SASR 45; R v Von Einem (1985) 38 SASR 207, discussed.
Australian Securities Commission and Investments Commission v Rich (2005) 218 ALR 764; Clark v Ryan (1960) 103 CLR 486; Cooper v Bech (No 2) (1975) 12 SASR 151; Frye v United States 293 F 1013 (1923); Murphy v The Queen (1989) 167 CLR 94; Paric v John Holland (Constructions) Pty Ltd (1985) 59 ALJR 844; R v Howard (2005) 152 A Crim R 7; R v Perry (1990) 49 A Crim R 243; Sydneyside Distributors Pty Ltd v Red Bull Australia Pty Ltd (2002) 55 IPR 354; Trade Practices Commission v Arnotts Ltd (No 5) (1990) 21 FCR 324; Transport Publishing Co Pty Ltd v Literature Board of Review (1956) 99 CLR 111; Wolper & Poole (1972) 2 SASR 419, considered.

R v BJORDAL
[2005] SASC 422
Court of Criminal Appeal: Debelle, Besanko and Vanstone JJ

DEBELLE J: The appellant was convicted after trial by jury in the District Court of causing death by dangerous driving. He appeals against that conviction.
The main grounds of appeal relate to evidence given by a police officer, Sergeant Mills, as to the likely speed of the appellant’s vehicle at the time of the accident. Those grounds are:
1.That the trial judge erred in failing to grant a voir dire hearing to determine the admissibility of the evidence of Sergeant Mills.
2.That the trial judge erred in admitting the evidence of Sergeant Mills as to the likely speed of the appellant’s vehicle.
3.That the trial judge erred in failing to direct the jury or provide assistance to the jury in their consideration of the evidence given by Sergeant Mills as to the likely speed of the appellant’s vehicle having regard to
(a) the failure by the prosecution to qualify Sergeant Mills as an expert on this topic; and
(b) the evidence of a Mr Hall that there was no scientific basis for the application by Sergeant Mills of a formula to determine the speed of the appellant’s vehicle given the road conditions that confronted the appellant.
There was a fourth ground of appeal that the trial judge had erred in reversing the onus of proof in his direction to the jury.
An Accident Causes Death
At about 10.15 pm on 24 May 2002, the appellant was driving his Toyota utility along Sheoak Road, Crafers West, heading towards Belair. He had a passenger in the utility, Mr Neil Kirkley. As the appellant drove downhill and around a right‑hand bend in the road, he lost control of his utility and it overturned trapping both the appellant and Mr Kirkley inside. After the appellant’s vehicle had overturned, it crossed the road and came to rest against a tree. There was loose gravel covering the bitumen on the left‑hand side of the carriageway of the bend. Mr Kirkley later died from the injuries he sustained in the crash.
The Prosecution Case
The prosecution case was that, during the afternoon of 24 May 2002, the appellant and Mr Kirkley had been drinking at two hotels. The second was the Crafers Hotel. It was alleged that, when they left the Crafers Hotel, the appellant’s ability to drive was impaired by the alcohol he had consumed. The prosecution alleged that the appellant had driven in a manner dangerous to the public in that he had driven at an excessive speed along Sheoak Road and in a reckless manner so that he was unable to control his vehicle as he tried to negotiate the bend in Sheoak Road.
The Appellant’s Case
The appellant’s case was that his ability to drive was not impaired by the alcohol he had had to drink but that he had been guilty of an error of judgment in driving a little too quickly when negotiating the bend and that error had been compounded by the loose gravel on the bitumen or an under‑inflated tyre on the left‑hand side of the utility or a combination of both.
An Estimate of Speed
The prosecution had given notice that it intended to call Sergeant Mills to prove an estimate of the speed at which the appellant was driving just before he negotiated the bend on Sheoak Road. Sergeant Mills had estimated that the appellant was then driving his utility at a speed of between 67 and 91 kilometres per hour. The estimate had been calculated by using a formula which had been developed to determine the speed of vehicles travelling on a bitumen surface.
The Estimate is Challenged
The appellant caused a Rule 9 application to be filed applying, among other things, for an order excluding the evidence of Sergeant Mills as to his estimate of the speed of the appellant’s utility. The application challenged the applicability of the formula which Sergeant Mills had used and contended that Sergeant Mills lacked the necessary expertise to make an adjustment to one of the components of the formula. The appellant submitted that the formula used by Sergeant Mills was inapplicable because it had been developed for the purpose of estimating the speed of vehicles travelling on bitumen surfaces. One component of the formula was the co‑efficient of friction between the tyres and the bitumen surface. The co‑efficient of friction had been determined after extensive empirical testing. The formula was inapplicable in this case because the loose gravel on the road affected the co‑efficient of friction. Sergeant Mills had made adjustments to allow for the loose gravel but the appellant challenged both the validity of those adjustments and the expertise of Sergeant Mills to adjust the co‑efficient of friction to allow for the loose gravel. The appellant gave notice that he intended to call Mr C T Hall, a mechanical engineer with experience in accident reconstruction, to prove that the formula was inapplicable, that there is no scientifically established formula which could be used in the circumstances of this case, and to challenge the adjustments made by Sergeant Mills. The appellant also applied for a voir dire hearing to determine the expertise of Sergeant Mills. The trial judge dismissed the application and ruled that Sergeant Mills would be permitted to give evidence as to his estimate of the speed of the appellant’s utility. No reasons were given for the ruling.
The application to exclude the evidence of Sergeant Mills was not renewed at the trial because counsel for the appellant understood that the ruling made on the application for a voir dire hearing was to the effect that Sergeant Mills was qualified to give evidence of his calculation and the evidence was admissible.
There were, therefore, two grounds on which the appellant contended that Sergeant Mills should not give evidence. The first was that the formula was in this case inapplicable, if not scientifically unsound. The second was that Sergeant Mills had no expertise to make the adjustment he had made. The appellant submitted that the calculation of speed by Sergeant Mills was so fundamentally flawed that it should not be led.
The Prosecution Evidence
The prosecution presented Sergeant Mills to the jury as an expert qualified to express an expert opinion as to the calculation of speed based on skid marks or tyre marks.
Sergeant Mills is a member of the Crash Reconstruction Unit with the Major Crash Investigation Section of the Police Department. He began working in that unit in 1989. Before being employed in that unit, he had participated in a four week course in accident investigation conducted by the Major Crash Investigation Section. Since then, he has investigated in excess of 100 motor vehicle accidents. Sergeant Mills has undertaken a TAFE course and a further course of instruction on survey techniques. In 1995 he attended an international conference in Queensland on accident investigation, reconstruction, interpretation, and the law. That conference was organised by the Association of Australasian South Pacific Crash Investigators and by the Queensland University of Technology. He attended similar conferences in 1997, 1999, 2000 and 2002. In 1998 he undertook an advanced accident investigation course organised by the Police Department and conducted under the auspices of the Texas University. In 2001 he attended a two week course of advanced instruction conducted in Wellington, New Zealand, by the Royal New Zealand Police College. In April and May 2002 he attended an eight week course conducted by the North‑Western University Centre for Public Safety at Illinois in the United States of America. In May 2002 he attended a seminar organised by the Institute of Traffic Accident Investigation at Ashbourne in England. That seminar dealt with high speed and fixed object crashes.
The formula used by Sergeant Mills enables calculation of what is called the “critical curve speed”. The critical curve speed is the maximum speed at which a vehicle will be able to negotiate a bend without slipping. The formula is sometimes called the “critical speed formula”. For convenience, I will call it “the formula”. It comprises a number of components, some of which are variable.
One of the variables is the radius of the bend around which the vehicle is travelling. Another is the co‑efficient of friction between the tyres of the vehicle and the surface on which it is travelling. The radius of the bend is capable of being determined objectively by measurement and calculation. That was common ground. It was also common ground that the co‑efficient of friction is an essential component of the equation. It was the appellant’s case that, unlike other variables, the co‑efficient of friction was not capable of objective measurement or calculation but could only be determined by empirical tests and observation. In the formula used by Sergeant Mills, the co‑efficient of friction was that for cars travelling in a straight‑line skid on a clean bitumen surface. It has been established empirically by extensive testing.
The prosecution contended that it was appropriate for Sergeant Mills to make adjustments to the co‑efficient of friction to take into account the gravel on the road by using certain tables and his considered estimate. The appellant disputed that relying on the fact that, in the circumstances of the accident, the co‑efficient of friction could only be determined by extensive empirical testing.
The determination of the co‑efficient of friction in this case was complicated by the fact that there was loose gravel on top of the bitumen surface on the left‑hand side of the road. The co‑efficient of friction of a level bitumen surface ranges between 0.65 and 0.75 for car tyres. That figure has been determined as a result of empirical observations of a number of tests of vehicles skidding on level bitumen surfaces. Light truck tyres were fitted to the appellant’s Toyota utility. Testing has demonstrated that the co‑efficient of friction of light truck tyres is about 0.1 less than that for car tyres. Sergeant Mills made that adjustment for the light tyre trucks and that adjustment is not in dispute.
Sergeant Mills then purported to make an allowance for the loose gravel on the bitumen surface on the left‑hand side of the road. He made an allowance of 0.2 at the lower end and 0.1 at the upper end of the range for that gravel. This resulted in an estimate of the range of the co‑efficient of friction being between 0.35 and 0.55. His evidence was that he was making a conservative adjustment, that is to say, an adjustment which would produce a lower rather than a higher speed. Those adjustments were made using published articles and tables in textbooks that give some guide as to the co‑efficient of friction that can be expected with loose gravel. Neither the articles nor the tables on which his adjustment was based were produced. Plainly, there are many kinds of gravel surfaces. The materials to which Sergeant Mills referred concerned what he described as “a hard packed base” which he assumed to be loose gravel on a hard packed base.
It was necessary also to make an adjustment to the co‑efficient of friction to allow for the effect of the slope of the road in the direction in which the utility slipped. Sergeant Mills adjusted the estimate of the co‑efficient of friction down to take the slope into account. This produced a range between 0.266 and 0.466. Using those values and his calculation of the radii of the tyre marks, he calculated that the speed of the appellant’s utility was between 67 and 91 kilometres per hour.
Sergeant Mills acknowledged in evidence in chief that the factor in the equation which is the least certain is the co‑efficient of friction. In cross‑examination, he admitted that he had accepted what had appeared in tables published in text books. He also took into account some skid tests he had made on gravel surfaces. However, he admitted that he had conducted no more than three to seven such tests.
Sergeant Mills acknowledged that there had been little empirical testing of the co‑efficient of friction when a vehicle is sliding round a bend on a loose gravel surface. He said that he had allowed for that by taking a co‑efficient of friction lower than the lowest shown on any table.
The Appellant’s Evidence
The appellant called Mr C T Hall in answer to the evidence of Sergeant Mills. Mr Hall has an Honours Degree in Mechanical Engineering from the University of Adelaide conferred in 1974. Thereafter, he worked with the Road Accident Research Unit at the University of Adelaide until 1978. That unit consisted of a multi‑disciplinary team which studied motor vehicle accidents in metropolitan Adelaide. Mr Hall’s task was to reconstruct accidents. Since 1978 he has practised as a consultant. For the first seven years (1978 - 1985), he was a consultant at the Australian Mineral Development Laboratories where he was involved, among other things, in the reconstruction of motor vehicle accidents. Since 1985 he has practised as a consultant on his own account in reconstructing motor vehicle accidents and in motor racing circuit design and motor racing safety. He expresses opinions in respect of about 120 – 150 motor vehicle accidents in each year.
Mr Hall’s evidence was that it was not appropriate to take the formula applicable to bitumen surfaces, which had been developed as a result of empirical observation and testing, and to apply it directly to the case of a vehicle which has tyres running on a gravel surface and where the vehicle is yawing. He said that the co‑efficient of friction used in the formula had been developed in an empirical way for bitumen surfaces after extensive testing, to use his words, “hundreds and hundreds and hundreds of tests … over a period of many years”. Because tyres act differently on dirt surfaces, it was necessary, he said, to conduct tests to determine the co‑efficient of friction for such surfaces. However, because dirt surfaces vary so much, it cannot confidently be said that one dirt surface is the same as another. Similarly, the characteristics of gravel surfaces are not consistent with those of bitumen surfaces, especially for a vehicle which is yawing. It was not, therefore, possible to apply the formula to this accident even if a deduction was made to allow for the reduced friction by reason of the loose gravel. It was, he said, scientifically unsound simply to seek to adjust the co‑efficient of friction as Sergeant Mills had done. There was no scientific basis for the adjustment which he had purported to make.
Mr Hall re‑inforced his evidence by referring to tests he had conducted in 2001 with the Department of Mechanical Engineering at the University of Adelaide for the purpose of determining whether it was possible to correlate a straightforward skid test to the motion of a car which was yawing on a range of surfaces other than a clean bitumen surface. The surfaces on which tests were conducted included a gravel surface, a dirt road and a combination of dirt and grass. The tests showed there was no direct correlation. Because vehicles will react differently on different surfaces, it is not possible to adjust the co‑efficient of friction for bitumen surfaces to allow for the case of a vehicle yawing on a gravel surface. Although one can make the adjustment to that co‑efficient of friction to produce a conservative answer, it is not possible to determine what the correct adjustment should be. It is necessary to obtain a good deal more data before one can be confident what that factor should be. The tests he had conducted showed that there was a potential to over‑estimate the speed for a yawing vehicle on a gravel surface by as much as 15 to 20 per cent.
Shortly stated, the effect of Mr Hall’s evidence was that it was not possible in the circumstances of this accident to rely on the formula in order to estimate the speed at which the appellant’s utility entered the corner. Even if the formula were to be applied, it was not possible accurately to determine the adjustment which should be made to the co‑efficient of friction to allow for the gravel on the surface of the road although rough estimates might be made. For that reason, he said, assuming you could apply the formula, the adjustment made by Sergeant Mills might be wrong. He was not prepared to say that the calculations by Sergeant Mills were wrong but he was firm in his view that it would not be scientifically correct to apply the formula in the circumstances of this accident.
Mr Hall said that by plotting the path of the utility through the yaw it was possible to determine more accurately its speed as it entered the bend. A shorter yawing path, he said, would indicate less decrease in speed along that path. Because of the circumstances surrounding the rolling of the vehicle, he estimated that the utility was not travelling at a great deal over 50 to 60 kilometres per hour at the time it began to roll over. Accordingly, it was very unlikely to have been travelling at 90 kilometres per hour when it entered the bend. He acknowledged that his was a conservative estimate which was not necessarily accurate. However, he was firm that the utility was very unlikely to have been travelling as fast as either 80 or 90 kilometres per hour at the start of the yaw. He conceded that, immediately prior to entering the bend, the appellant’s vehicle might have been travelling at 60 to 75 kilometres per hour.
The basis of his criticism was that the relationship between straight‑line and curved, yawing skids on gravel surfaces could only be known after a great deal of testing. No such testing has been done anywhere in the world. It was, he said, poor science to seek to use this formula that had not been verified on gravel surfaces and could only be verified after considerable testing. Although there were published figures for the co‑efficient of friction for gravel surfaces, they were the results of tests of straight‑line skidding which were inapplicable in this case because the appellant’s utility had slipped into a yawing motion.
Relevant Principles

The conditions governing the admissibility of evidence tendered as expert opinion were expressed by Heydon JA in Makita (Australia) Pty Ltd v Sprowles (2001) 52 NSWLR 705 at [85] in these terms:
In short, if evidence tendered as expert opinion evidence is to be admissible, it must be agreed or demonstrated that there is a field of “specialised knowledge”; there must be an identified aspect of that field in which the witness demonstrates that by reason of specified training, study or experience, the witness has become an expert; the opinion proffered must be “wholly or substantially based on the witness’s expert knowledge”; so far as the opinion is based on facts “observed” by the expert, they must be identified and admissibly proved by the expert, and so far as the opinion is based on “assumed” or “accepted” facts, they must be identified and proved in some other way; it must be established that the facts on which the opinion is based form a proper foundation for it; and the opinion of an expert requires demonstration or examination of the scientific or other intellectual basis of the conclusions reached: that is, the expert’s evidence must explain how the field of “specialised knowledge” in which the witness is expert by reason of “training, study or experience”, and on which the opinion is “wholly or substantially based”, applies to the facts assumed or observed so as to produce the opinion propounded. If all these matters are not made explicit, it is not possible to be sure whether the opinion is based wholly or substantially on the expert’s specialised knowledge. If the court cannot be sure of that, the evidence is strictly speaking not admissible, and, so far as it is admissible, of diminished weight. And an attempt to make the basis of the opinion explicit may reveal that it is not based on specialised expert knowledge, but, to use Gleeson CJ’s characterisation of the evidence in HG v The Queen (at 428 [41]), on “a combination of speculation, inference, personal and second‑hand views as to the credibility of the complainant, and a process of reasoning which went well beyond the field of expertise”.
The decision in Makita has been consistently followed since: see, for example, Australian Securities & Investment Commission v Rich (2005) 218 ALR 764 and R v Howard (2005) 152 A Crim R 7. In Sydneyside Distributors P/L v Red Bull Australia P/L (2002) 55 IPR 354, Branson J commented that the approach of Heydon JA seemed a counsel of perfection. However, as the Court of Criminal Appeal noted in R v Howard at 13 when Her Honour elaborated her reservations, she noted that the existence of a field of specialised knowledge was something which might be assumed in cases where evidence is adduced without objection. That is not the position here.
The passage quoted from Makita identifies several conditions. For present purposes it is sufficient to refer to the following:
1.there must be a field of specialised knowledge;
2.there must be an identified aspect of that field in which the witness has demonstrated an expertise;
3.the opinion must be based on the expert knowledge of the witness;
4.so far as opinion is based on facts observed or assumed, those facts must be identified and proved; and
5.it must be established that the facts on which the opinion is based form a proper foundation for it.
I turn to examine the application of those conditions to the issues in this case.
The principles by which a court decides whether the opinion which the expert seeks to address forms part of a field of specialised knowledge were examined by King CJ in R v Bonython (1984) 38 SASR 45 at 46 – 47. He said:
Before admitting the opinion of a witness into evidence as expert testimony, the judge must consider and decide two questions. The first is whether the subject matter of the opinion falls within the class of subjects upon which expert testimony is permissible. This first question may be divided into two parts: (a) whether the subject matter of the opinion is such that a person without instruction or experience in the area of knowledge or human experience would be able to form a sound judgment on the matter without the assistance of witnesses possessing special knowledge or experience in the area, and (b) whether the subject matter of the opinion forms part of a body of knowledge or experience which is sufficiently organized or recognized to be accepted as a reliable body of knowledge or experience, a special acquaintance with which by the witness would render his opinion of assistance to the court. The second question is whether the witness has acquired by study or experience sufficient knowledge of the subject to render his opinion of value in resolving the issues before the court.
That principle had been expressed earlier in Clark v Ryan (1960) 103 CLR 486. In Wolper v Poole (1972) 2 SASR 419 at 421 Bray CJ had summarised the principle in these terms:
Evidence of the opinions of expert witnesses should only be received when the subject matter so far partakes of the nature of a science as to require a course of previous experience or study in order to attain a knowledge of it and when the witness in question has qualified himself by such previous experience or study.
See also Transport Publishing Co Pty Ltd v Literature Board of Review (1956) 99 CLR 111 at 119 and Murphy v The Queen (1989) 167 CLR 94 at 111.
Accident investigation has become an organised branch of knowledge in which there is an organised course of study: Wolper v Poole (supra). However, that does not necessarily lead to the conclusion that a person who has studied and gained experience in that field is qualified to express an opinion on all issues relating to motor vehicle accidents: Cooper v Bech (No 2) (1975) 12 SASR 151 at 153. The different decisions in the following list of cases illustrate this conclusion: Clark v Ryan (supra), Weal v Bottom (1966) 40 ALJR 436, Demasi v Fraser [1965] SASR 284, Fisher v Brown [1968] SASR 65, McKay v Page & Sobolski (1971) 2 SASR 117, Mattioli v Parker (No 2) [1973] Qd R 499, and R v Faulkner [1987] 2 Qd R 263. Those decisions also illustrate the second condition of the admissibility of evidence of expert opinions, namely, that there must be an identified aspect of that field in which the witness has demonstrated expertise.
The second condition is what King CJ called “the second question” in the passage already quoted from R v Bonython. Immediately after that passage, King CJ went on to examine how the methods used by the witness in reaching his opinion might assist in the resolution of the two questions he had identified. His observations also assist in determining the third condition that the opinion must be based on the expert knowledge of the witness. He said (at 47):
An investigation of the methods used by the witness in arriving at his opinion may be pertinent, in certain circumstances, to the answers to both the above questions. If the witness has made use of new or unfamiliar techniques or technology, the court may require to be satisfied that such techniques or technology have a sufficient scientific basis to render results arrived at by that means part of a field of knowledge which is a proper subject of expert evidence. Examples of cases in which that question arose are The Queen v Gilmore, The Queen v McHardie and Danielson and United States v Williams. An investigation of the methods adopted by a witness may be relevant to an assessment of his qualifications as a witness if such an investigation might reveal that the witness has “posing as an expert made assertions that are contrary to proved scientific facts or to the known phenomena of nature, thus exposing his ignorance of the learning he professed” (Commissioner for Government Transport v Adamcik, per Windeyer J at p 306), or that the witness has adopted methods which are so unscientific as to expose that ignorance. Where the witness possesses the relevant formal qualifications to express an opinion on the subject, an investigation on the voir dire of his methods will rarely be permissible on the issue of his qualifications. There may be greater scope for such examination where the alleged qualifications depend upon experience or informal studies. The trial judge must have a wide discretion as to what may be investigated on the voir dire and the scope for interference by an appellate court with the way in which the discretion is exercised must be limited. Generally speaking, once the qualifications are established, the methodology will be relevant to the weight of the evidence and not to the competence of the witness to express an opinion. The suitability and adequacy of the methods used may well be themselves a matter of expert opinion. (Citations omitted)
An important question in this case is whether Sergeant Mills had the expertise to determine what figures should be adopted for the co‑efficient of friction in the formula. Another concerns the methods he adopted when making his calculation. I will return to these questions.
The fourth and fifth conditions are closely related. Both are aspects of what King CJ called “the methods used by the witness”. Since opinion evidence involves the drawing of inferences and conclusions from facts, the admissibility of such evidence depends upon proof or admission of the facts on which the opinion is based: R v Perry (1990) 49 A Crim R 243 per Gleeson CJ at 249; Paric v John Holland (Constructions) Pty Ltd (1985) 59 ALJR 844 at 846. This principle is an application of the principle noted in § 558 of Wigmore on Evidence (1979 Chadbourne Revision) that observation or knowledge of the subject of the evidence is one of the essential elements of the qualification to give evidence. Later, at § 672 Wigmore spelled out the application of the principle in the context of “hypothetical questions” in these terms:
1. Testimony in the shape of inferences or conclusion always rests on certain premises of fact. That which has been called observation, serving as the basis of belief in matters directly cognisable by the senses – as, the facts of an affray, a conversation, a trespass, and the like – is here replaced by what may be called a consideration of the premise. If the witness has not considered or had in mind these premises, his inference or opinion is good for nothing. 2. These premises, a consideration of which is essential to the formation of the conclusion or opinion, must somehow be supplied to the jury by testimony. The same witness may supply both premises or conclusion; or one witness may supply the premises and another the conclusion. The two are not necessarily connected. 3. If the latter method is chosen, and a witness is put forward to testify to the conclusion, the premises considered by him must be expressly stated, as the basis of his conclusion; otherwise, since his conclusion rests for its validity upon a consideration of the premises, if those premises are not made to accompany the conclusion, the tribunal might be accepting a conclusion for which the witness had considered premises found by the tribunal not to be true. 4. Hence, the premises must be stated hypothetically in connection with the conclusion; then, by other testimony, the material for determining the truth of the assumed premises may be furnished to the tribunal.
The key to the situation, in short, is that there may be two distinct subjects of testimony – premises, and inferences or conclusions; that the latter involves necessarily a consideration of the former; and that the tribunal must be furnished with the means of rejecting the latter if upon consultation they determine to reject the former, ie, of distinguishing conclusions properly founded from conclusions improperly founded. (footnotes omitted)
These remarks were adopted and applied by Beaumont J in Trade Practices Commission v Arnotts Ltd (No 5) (1990) 21 FCR 324 at 327, affirmed on appeal (1990) 24 FCR 313. Wigmore expressed the same proposition more shortly at § 1917 when he said that the witnesses must speak “as a knower, not merely as a guesser”.
This may be a somewhat roundabout way of demonstrating the fundamental principle of logic that conclusions rest on premises and the validity of the conclusion will depend on the correctness of the premise on which it is based.
In this case, the critical factual premise on which Sergeant Mills’ estimate of the speed of the appellant’s utility rested was the co‑efficient of friction of the tyres on the loose gravel. Sergeant Mills had identified that fact. The question was whether his adjustment was valid and whether he had the expertise to make the adjustment.
The Invalidity of the Adjustments.
There was no dispute that
(1)the co‑efficient of friction was a critical component in the formula;
(2)the co‑efficient of friction between car tyres and a bitumen surface had been determined by extensive empirical testing and that it was applicable to both straight‑line skids and yawing on a clean bitumen surface; and
(3)that the co‑efficient of friction had to be adjusted because of the loose gravel on the surface of Sheoak Road.
The evidence of Mr Hall positively demonstrated that the co‑efficient of friction applicable to the present case could not be determined by the simple application of the laws of physics or by theoretical deduction, and that the only means by which it was possible to determine the co‑efficient of friction was by extensive empirical testing. The formula enables a conclusion to be expressed as to the speed of a vehicle immediately prior to it commencing to skid. The conclusion will be valid only if the premises, that is to say, if each of the components in the formula are correct. One of the critical components of the formula was the co‑efficient of friction which could only be reliably included if a figure, based on empirical testing, was known. In the absence of such a figure, any estimate of the co‑efficient of friction was merely an arbitrary assessment, if not a guess, and, therefore, unreliable. It is, as Mr Hall said, bad science to proceed in this way without the data on which to make the estimate, particularly when it is not known if there is correlation between the information on which Sergeant Mills relied and a vehicle yawing on a gravel surface. Sergeant Mills was, therefore, purporting to make a scientific calculation in the absence of the correct data on which to base his calculation and purported to remedy the data by making adjustments which have no scientific foundation. For that reason the estimate of speed made by Sergeant Mills was unreliable and, therefore, inadmissible. Although Sergeant Mills had described his adjustments as conservative, they might not have been sufficiently conservative to allow for the yawing on a gravel surface. A further downward adjustment of the co‑efficient of friction would reduce his calculation of the speed of the appellant’s utility.
Mr Hinton who appeared for the prosecution on the appeal, submitted that the criticisms made by Mr Hall of Sergeant Mills’ assessment of the co‑efficient of friction went to the weight of that assessment and not to its admissibility. That submission must be rejected. The validity of the calculation of the speed of the appellant’s utility depends on the reliability of the components of that calculation. If one of the components is false, the calculation has no validity. It is, therefore, not a question of the weight of evidence but of the accuracy of the calculation. Either the calculation is correct or it is incorrect. There is no room for weighing differing opinions.
Mr Hinton relied on the fact that Mr Hall was not prepared to say that Sergeant Mills’ conclusion was wrong. The contention misconceives the effect of Mr Hall’s evidence. Mr Hall’s thesis was that the formula could not be used because one important component could not be established, other than by extensive empirical testing. He was not in a position, therefore, to say whether Sergeant Mills’ conclusion was correct or incorrect because there is no yardstick or standard by which the correctness or otherwise of the conclusion can be tested, short of empirical testing. It was not possible, therefore, for Mr Hall to proffer an opinion whether Sergeant Mills was correct or incorrect. It is not appropriate to describe Sergeant Mills’ estimate of the co‑efficient of friction as an informed estimate, because the nature of the exercise does not admit of estimates, informed or otherwise. One continues to return to the fundamental fact that the validity of the calculation of speed by use of this formula depends on the validity of each of the components in the formula.
For like reasons, Sergeant Mills’ assertion that he was making conservative adjustments could not assist the prosecution because it cannot be known whether his adjustments were sufficiently conservative.
Did Mills Have The Necessary Expertise?
The second question is whether Sergeant Mills had the necessary expertise to make the adjustments to the co‑efficient of friction. The effect of the evidence of Mr Hall was that no person is competent to make adjustments to the co‑efficient of friction as determined for bitumen surfaces to allow for yawing on other surfaces. It is not possible to calculate the co‑efficient of friction in such a case by use of the laws of physics or by any process of deductive reasoning. It can only be reliably achieved by extensive empirical testing. To adapt the words of King CJ in R v Bonython, the subject matter of the opinion which Sergeant Mills purported to express, namely, his adjustment to the co‑efficient of friction, was an opinion which did not form part of a body of knowledge or experience which had been sufficiently organised to be accepted as a reliable body of knowledge or experience. Although empirical testing had yielded a reliable body of knowledge for skidding and yawing on clean bitumen surfaces, sufficient testing had not been conducted to yield a reliable body of knowledge to determine the co‑efficient of friction for vehicles yawing on surfaces other than bitumen. For that reason alone, Sergeant Mills lacked the necessary expertise.
Conclusion
There are, therefore, two lines of reasoning which lead to the conclusion that the evidence of Sergeant Mills of his calculation of the speed of the appellant’s vehicle was inadmissible. One is that there is no body of organised knowledge or experience which would cause his opinion to be of assistance to the court. The other is closely related, namely, that the calculation was grounded on an unreliable premise so that it could not be of assistance to the court.
This was an instance where it was necessary for the trial judge to determine whether the prosecution should be permitted to lead evidence of the calculation of the speed of the appellant’s vehicle made by Sergeant Mills grounded as it was on the opinion of Sergeant Mills as to the co‑efficient of friction between the tyres of the appellant’s vehicle and the loose gravel on the surface of the bitumen on Sheoak Road. It was necessary for the judge to determine whether Sergeant Mills’ opinion was based on a body of knowledge or experience which was sufficiently organised and recognised to be accepted as a reliable body of knowledge or experience which would assist the jury. He also had to determine whether Sergeant Mills had the required expertise to express the opinion as to the co‑efficient of friction. The judge had been informed that the challenge to the calculation and to the expertise of Sergeant Mills to make the calculation was supported by evidence. For the reasons expressed in R v Bonython at 46 and 47 and in Makita (Australia) Pty Ltd v Sprowles at [85], this was a proper matter for enquiry on the voir dire.
For these reasons, the trial judge erred in failing to accede to the application of the appellant for a voir dire to determine the admissibility of the evidence of Sergeant Mills as to the likely speed of the appellant’s vehicle. For the same reasons, the trial judge erred in admitting the evidence of Sergeant Mills as to the likely speed of the appellant’s vehicle. The issue of the speed of the appellant’s vehicle was an important part of the prosecution case. The prosecution should not have been permitted to lead evidence of the calculation of that speed by Sergeant Mills. If that evidence had not been led, the evidence of Mr Hall would not have been led. The fact that the prosecution was permitted to lead inadmissible evidence as to speed has resulted in a miscarriage of justice. I would, therefore, allow the appeal.

Given these conclusions, it is unnecessary to address the third ground of appeal that the trial judge erred in failing to direct the jury or to provide assistance to the jury in their consideration of the evidence given by Sergeant Mills as to the likely speed of the appellant’s vehicle, having regard to the failure to qualify Sergeant Mills as an expert and the evidence of Mr Hall. If it had been necessary, I would have allowed the appeal on this ground. There was such a clear conflict between the evidence of Sergeant Mills and that of Mr Hall regarding both the suitability and the reliability of using the formula to calculate the speed of the appellant’s vehicle by reason of the issues as to the co‑efficient of friction that it was necessary for the trial judge to direct the jury on that conflict and the means by which to evaluate that evidence. The trial judge failed to provide that assistance. More significantly, he failed to direct the attention of the jury to the defence case as to the unreliability of the evidence of Sergeant Mills.
The conclusion I have reached renders it unnecessary also to consider the issue whether the learned trial judge erred by reversing the onus of proof in his direction. I simply note that, when the words complained of are read in context, it is clear that the judge did not reverse the onus of proof.
For all of these reasons, I would allow the appeal. I would set aside the verdict and the sentence and order a re‑trial.
BESANKO and VANSTONE JJ:
Introduction
Kieran Scott Bjordal appeals against his conviction in the District Court for causing death by dangerous driving.
The appellant complains that expert opinion evidence as to the speed of the appellant’s vehicle prior to collision was wrongly admitted and, in the alternative, that the Judge’s directions to the jury about that evidence were inadequate. He further complains that at one point in his directions the Judge reversed the onus of proof and that he failed to adequately put the defence case.
Background
On Friday, 24 May 2002, at about 11.00 pm, the appellant was driving a Toyota Hilux utility vehicle west along Sheoak Road at Crafers West. The vehicle was in good condition, although one tyre was found to be under-inflated after the collision, and possibly was before it. The appellant was carrying a passenger, Neil Kirkley, who died from injuries sustained as a result of the collision. Evidence in the nature of accident reconstruction established that the vehicle was travelling slightly downhill near the beginning of a right hand curve in the road when the appellant lost control. The car slid 22 metres and rolled 6 metres. The road was bitumen of generally good condition, although with an amount of stone and rubble to the left side. It was dry.
A blood sample was taken from the appellant about three hours after the collision. It gave a concentration of .109 grams alcohol per 100 mls of blood. Expert evidence was to the effect that given a steady drinking pattern continuing to shortly before the collision, the concentration then would have been about 0.10 grams percent.
Analysis
Was the evidence of speed properly admitted?
The appellant argues that the opinion evidence of Sergeant Mills as to the likely speed of the appellant’s vehicle during its passage around the bend before it left the road was inadmissible. The Judge declined to take evidence going to that issue on the voir dire and the appellant raised that decision as a ground of appeal. However, since the material relevant to admissibility was the same as that upon which the defence sought to discredit Sergeant Mills’ evidence before the jury, the question for determination is simply whether the evidence was admissible.
Sergeant Mills has no general scientific qualifications. However he is, to an extent, an acknowledged expert in the area of accident reconstruction. That expertise is based on informal tuition, reading, attending conferences and practical experience. He based his opinion on observations of marks left by the tyres of the accused’s vehicle in the 50 metres or so before collision, along with the characteristics of the stretch of roadway involved and the vehicle. He utilised that data in an equation, colloquially referred to as the “critical speed formula”, designed to establish the speed of a vehicle at a point along the length of such marks. That equation required input of the radius of the scuff marks, the coefficient of friction of the tyres of the vehicle against that road surface, as well as a value for gravity. The coefficient of friction was selected, not on the basis of any testing of the stretch of roadway in issue, but rather by use of data generated in published studies. The likely speed he arrived at was between 67 and 91 kilometres per hour.
The factors said at trial and on the appeal to complicate this issue were first, that a metre or so of the left extremity of the bitumen roadway where the appellant’s vehicle lost control bore a gravel, or metal, overlay and secondly, that the tyre marks under consideration were not straight line “skid” marks, but were “scuff marks” or “rotating tyre marks” made by the vehicle in yaw. The appellant presented evidence at trial from Mr Hall, an acknowledged expert, trained as a mechanical engineer, which called into question the applicability of the formula – said to have been developed for bitumen surfaces – to bitumen surfaces with such an overlay. Mr Hall further criticised the adjustment made by Sergeant Mills, on account of the gravel overlay, to the coefficient of friction normally employed for bitumen.
The appellant argues that the purported application of the critical speed formula to a bitumen plus gravel surface, without there being any empirical evidence to support it, and the absence of any scientific or empirical basis for the allowances made to the coefficient by Sergeant Mills, took the proffered opinion outside any body of knowledge or experience sufficiently organised to be accepted as reliable and, therefore, beyond any subject matter upon which the witness should have been permitted to offer an opinion. In making that submission counsel relied principally on the decision of this Court in R v Bonython (1984) 38 SASR 45. (See also Frye v United States 293 F 1013 (1923).)
In Bonython, King CJ said that before opinion evidence may be admitted as expert testimony, a judge must consider and decide two questions. The first question may be divided into two parts, the first of which is (at 46 – 47):
… whether the subject matter of the opinion is such that a person without instruction or expertise in the relevant area of knowledge or human experience would be able to form a sound judgment on the matter without the assistance of witnesses possessing special knowledge or experience in the area.
There was no dispute that that condition was met in this case.
The second part of the first question was stated by King CJ in the following terms (at 47):
… whether the subject matter of the opinion forms part of a body of knowledge or experience which is sufficiently organized or recognized to be accepted as a reliable body of knowledge or experience, a special acquaintance with which by the witness would render his opinion of assistance to the court.
The question of whether this second condition was satisfied is more difficult. According to the evidence of Mr Hall, there is a sufficiently organised or recognised body of knowledge or experience in relation to the use of the equation where skid marks on a bitumen or gravel road surface, or scuff marks on a bitumen surface are in issue. However, there is not a sufficiently organised or recognised body of knowledge or experience in relation to the use of the equation where the marks are the scuff marks of a vehicle in yaw on a gravel surface; still less on a bitumen surface with a gravel overlay.
It is necessary to descend into a little more detail in order to fully understand the attack on Sergeant Mills’ evidence.
Mr Hall asserted that the critical speed equation had been developed by means of analysis of a wealth of empirical evidence gathered from testing on bitumen surfaces. It was not so much reliant on the laws of physics, he said, as upon that empirical data. It was found that the equation could be applied, not only to skid marks, but also – and without modification – to scuff marks made by a vehicle in yaw on bitumen. That was so despite the fact that different dynamics were at work. Where straight line skids were concerned, the retarding force was “pure friction”. Where the vehicle was in yaw, the movement was of the rolling tyres of a turning vehicle. However, Mr Hall’s evidence was that it turned out that there was direct (and we take him to have meant one to one) correlation between the respective retarding forces. Therefore, no modification to the equation was required. He expressed the view that the same would not necessarily hold good for gravel or dirt surfaces. There, the formula itself might require the input of another factor. Indeed, he said that testing in which he had been involved suggested that the correlation on dirt surfaces was other than direct.
Mr Hall said that even if the equation could be used, a separate difficulty arose in respect of Sergeant Mills’ selection of a coefficient of friction for the bitumen with gravel overlay. Sergeant Mills’ evidence was that he took the accepted range applicable to bitumen for car tyres (0.65 – 0.75) and then made adjustments to it for the relevant tyres being “light truck tyres”, the gravel overlay and the gradient of the road. The allowance for the surface gravel was 0.2 at the lower end and 0.1 at the upper end. Mr Hall asserted that this adjustment only purported to give a coefficient for a straight line skid on dirt or, as we follow his evidence, gravel. He said there was no basis for using such an adjusted coefficient for a vehicle travelling on a near circular path on a moving surface, such as gravel. Mr Hall was critical of any adjustment being made without a scientific basis to justify it. Sergeant Mills had not offered such a basis. Indeed, according to Mr Hall, no single figure could apply to all such gravel overlays, since the extent of and shape of the gravel would be variable. A further complication was that only the nearside wheels of the appellant’s car would have encountered gravel.
Unfortunately, because of the state of the evidence, Sergeant Mills’ answers to these various criticisms of his work are neither clear nor comprehensive. Nor was there any robust answer to Mr Hall’s contention that two separate problems presented themselves. In relation to the application of the critical speed formula itself to surfaces other than bitumen, his response was that he could not see why the same principles would not apply equally. To a non-scientist, such an answer might have an attraction. After all, if the equation were founded in Newton’s Second Law, as was suggested, then the translation of the equation from one surface to another would seem to be unexceptional. However, it does not seem to us that Sergeant Mills purported to specifically address Mr Hall’s argument that a new factor might need to be imported to cater for the absence – if indeed there is an absence – of a direct correlation as between a straight skid on gravel or dirt, as opposed to the movement of a vehicle in yaw on the same surface. There was no attempt to grapple with the effect, if any, of the nearside tyres alone encountering gravel.
Much the same can be said of Sergeant Mills’ answer to criticism of his method in quantifying the reduction to the bitumen coefficient of friction and then applying it to the road surface under consideration. His only response to the questions directed at how he arrived at a particular reduction was to assert that at all times he had been conservative and so used figures which would lead to a lower speed estimate. However, that is not really the point. In our view, as the evidence stood, he did not demonstrate that there was any reliable body of knowledge or experience which could justify his selection of an appropriate coefficient of friction. Consequently, we do not think the issue of whether there is a sufficiently organised or recognised body of knowledge or experience in relation to the use of the equation for scuff marks on a road surface such as this one was fully explored. That may have come about because a voir dire was not held and at the trial the focus of the parties was on leading the evidence relevant to their respective cases. Although that reservation as to whether the issue was fully explored at trial remains, on the evidence as led by the prosecution it was not established that this second condition for the admissibility of the opinion evidence was met.
The next question identified by King CJ in Bonython is whether the witness had acquired by study or experience sufficient knowledge of the subject to render his opinion of value in resolving the issues before the Court. In our opinion, however the earlier inquiries are resolved, this question must be answered against the admission of Sergeant Mills’ opinion as to the likely speed of the vehicle. With respect, the evidence of Sergeant Mills did not establish that even if there was a proper scientific basis for applying the formula to these road conditions, he had the necessary expertise to perform that task.
It is one thing for a person without theoretical qualifications to acquire a level of expertise in a given field where the precepts are clear and to be permitted to express opinions within that area. It is quite another thing for that person to then purport to deal with factual variations which are outside his mainstream expertise and to use judgment to accommodate them. In our view there is always a potential danger in using non-scientific personnel to perform tasks which require an objective and a scientific approach to the interpretation of data and which often require a grasp of general scientific principle.
We were referred, in argument, to R v Clarke (2003) 87 SASR 203. In that case a forensic scientist was allowed to give evidence as to the method he used to reconstitute a sample of blood which had denatured, so that he might analyse its alcohol concentration. The method he employed was not one in common usage in the Forensic Science Centre, but he expressed the view that it was a valid means of producing a result within certain tolerances. The court held that the fact that the methodology used was unusual did not mean that the scientist could not give evidence of his results. Those matters went only to the weight of the evidence. In our view, the contrast between such a case and the appellant’s is that between a properly qualified and experienced scientist, working within a scientific institution and applying the protocols of that institution, and further, using his scientific knowledge to accommodate unusual circumstances associated with his testing, as opposed to a person who has a narrow, albeit well developed band of expertise within a wider field of learning, but who does not demonstrate the experience or learning to move beyond the boundaries of that field, or to justify his conclusions in a court setting.
In terms of this case, therefore, our conclusion is that accident reconstruction and, within that field, calculating speed from tyre marks, is a subject which forms part of a body of knowledge which is sufficiently organised and recognised to be accepted as reliable, and is therefore a proper subject for expert testimony. However, Sergeant Mills’ evidence failed to demonstrate either that there was an acceptance among relevant authorities that the critical speed equation could be applied to tyre marks left by a vehicle in yaw on a bitumen surface with a part gravel overlay, or, even if there were, that he was qualified to so apply it and to justify his methodology. Therefore we find that the evidence was, in this case, wrongly admitted.
It will have been noted that the estimate of speed provided by Sergeant Mills was an extremely wide one. At its lower end it was not far from an indicative minimum speed arrived at by Mr Hall using a different method. It would not be surprising if, having regard to the state of the evidence, the jury was not inclined to place any emphasis on Sergeant Mills’ evidence. However, it is impossible to be sure of that. Particularly having regard to the wide ranging estimate before it, the jury could have determined that taking a midpoint was a safe course. In those circumstances, it cannot be said that no substantial miscarriage of justice has occurred.
Were the directions as to the evidence of speed sufficient?
In view of our conclusion that the evidence was wrongly admitted, there does not seem to be any point in discussing the directions given in respect of it. However, because the other grounds raise issues of importance, we propose to deal with them.
Was the onus of proof reversed?
The Judge gave directions as to the onus of proof in unexceptional terms. No criticism was levelled at those general directions. He further advised the jury that if, in the course of his summing up, he used words such as “proved” or “satisfied”, they were to understand that he would mean proof or satisfaction beyond reasonable doubt. In directing the jury as to what the Judge described as the third element of the charge, being causation, the Judge gave what the appellant suggested was a misdirection. The direction was as follows:
So, if you came to the conclusion, for example, that some other circumstance, like the gravel on the side of Sheoak Road, or the under-inflated rear tyre – if you are satisfied that it was under-inflated prior to the accused’s approach to the bend in Sheoak Road – was to some degree responsible for the accident, but that the accused’s driving was still a substantial cause of the accident and the death, that would establish the third element, even though other factors may have been involved.
It was upon the emphasised words within that direction that counsel for the appellant focussed.
We consider that the direction is technically correct. That is so because provided the jury was satisfied that the appellant’s manner of driving was a substantial cause of the death, its attitude to other contributing causes, no matter how confidently reached, would be immaterial. If the direction has a vice, it is that it could be seen to imply to the jury that factors which on one view might favour the defence – such as one of the tyres on the vehicle being under-inflated – might not be relevant unless the jury achieved a state of satisfaction about them. We are satisfied that the jury would not have been led into error by any such implication. For one thing, it would take a fairly subtle mind to draw that inference from a direction making a quite different point. But further, such an inference could not stand alongside the clear directions as to onus which the jury received, including that the accused did not have to prove anything.
Was the defence case adequately put?
Mr Edwardson, for the appellant, submits that the treatment of the defence case in the summing up was inadequate. In particular, he puts that in merely describing the defence as amounting to a contention that the prosecution had not proved the charge, the Judge overlooked the more positive position of the defence, namely that in the presence of the gravel on the road and proof of the low tyre pressure in the left rear tyre there were “innocent explanations for the accident”. Further, he pointed to the Judge’s failure to refer specifically to those two matters in his encapsulation of the defence.
Mr Edwardson made no complaint of the Judge’s summary of Mr Hall’s evidence or of his summary of the other defence witness, the appellant’s sister, who spoke of noting the appellant’s condition earlier in the evening of the collision.

The nature of the duty of the trial judge to put the defence case was summarised in R v Von Einem (1985) 38 SASR 207, at 216 per King CJ:
Generally speaking … [putting the defence case] … means no more than that [the judge] must state the substance of the defence case and, if appropriate, explain its bearing upon the legal issues in the case. The judge is not obliged to refer to the evidence called by the defence or to repeat the arguments of defence counsel. He may do so, of course, but that is a matter for his discretion. What is important is that the defence should be fairly and impartially presented to the jury. What a fair and impartial presentation involves in a particular case depends very much upon the legal issues in the case, the nature of the defence, the evidence called in support of it and the structure of the summing up.
A broadly similar statement of principle by the High Court, though relating to the Judge’s treatment of both cases, is found in Domican v The Queen (1992) 173 CLR 555, 5671. The Court observed that whether an evidentiary matter or argument must be mentioned turns on whether such a reference is necessary to ensure that the jurors have sufficient understanding of the evidence to enable them to fulfil their duty.
In this case the Judge chose to summarise the evidence of each witness, including the defence witnesses, rather than adopting an analysis of the various issues raised. Since upon interview by the investigating officer the appellant claimed no recollection of the events leading to the collision, and because he gave no evidence, the only material bearing on the event coming directly from the appellant was in the form of general statements he made to the investigating officer to the effect that the location of the accident involved a dangerous corner where the roadway often collected gravel and where there had been a number of accidents. The Judge related that evidence in the course of his witness summary. The topic of that gravel was also prominent in the evidence of the investigating officer in describing the roadway and in the evidence of an off duty police officer who lived adjacent to the accident scene. In summarising their evidence, the Judge referred to that topic. Similarly, in his summary of the examining mechanic’s evidence, he reminded the jury of the pressures in each tyre of the appellant’s vehicle and he reiterated the evidence of Sergeant Mills to the effect that the low tyre pressure, if present prior to the incident, might have caused the tyre to slip onto its side and in that way have led to, or contributed to, a loss of control.
These issues arose on the prosecution case. There was no direct evidence that either had played a critical part, or indeed any part, in the accident. They were matters for the jury to consider, along with all the other evidence, in determining whether the prosecution had proved that the accused was driving dangerously and that such driving led to the collision. In those circumstances we do not consider that the Judge can be criticised for dealing with them in the course of his treatment of the prosecution, as opposed to the defence, case. The fact is they were thoroughly explained. We consider that the Judge’s encapsulation of the defence case – that the prosecution had not discharged the onus upon it – was correct. Further, we think that the Judge’s presentation of the evidence to the jury was, in this case, apt to accurately and fairly put the respective cases for the prosecution and defence.
Conclusion
In view of our finding that the evidence did not disclose a proper basis for admission of the opinion evidence as to speed, we would allow the appeal, quash the conviction and order a retrial.