• Traffic Accident Reconstruction Testimony
  • May 20, 2003
  • Law Firms: Troutman Sanders LLP - Richmond Office; Troutman Sanders LLP - Atlanta Office
  • The Supreme Court's decision in Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999), dealt with the admissibility of evidence from experts other than scientists, such as engineers. It extended the admissibility principles set forth in Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), to embrace all sorts of expert testimony. One of the areas that would be covered by the Kumho Tire decision is traffic accident reconstruction testimony.

    Since the announcement of Kumho Tire in March 1999, court opinions citing and applying the decision have appeared at the rate of about 30 per month. Very few have, however, considered the admissibility of traffic accident reconstruction testimony.

    The authors of this article, a lawyer and an engineer, recently worked together in excluding accident reconstruction testimony offered by an expert witness in a Virginia federal court. The article discusses reported decisions shortly before and since Kumho Tire addressing the admissibility of such testimony. It then describes the experience of the authors as they and the court analyzed the reliability of an accident reconstruction opinion as to pre-impact vehicle speed and related issues in Smithers v. C&G Custom Module Hauling, Inc., Case No. 3:99cv633 (E.D.Va. 1999).

    Recent Challenges

    Shortly before the Kumho Tire decision was announced, the federal Fifth Circuit analyzed a challenge to the admissibility of the testimony of an accident reconstructionist. In Wilson v. Woods, 163 F.3d 935 (5th Cir. 1999), the defense challenged offered testimony that the defendant was exceeding the speed limit by eight miles per hour when the accident occurred. The trial court sustained the defendant's objection, and refused to admit the testimony. The appellate court affirmed the judgment for the defendant.

    Analyzing the expert's qualifications under Daubert and Rule 702 of the Federal Rules of Evidence, the trial court in Wilson v. Woods identified numerous factors cause concern. Although the expert had a master's degree in mechanical engineering, he never completed his doctorate. During his 25 years of consulting work, he had concentrated on fire reconstruction and investigation, not automobiles. Although the expert taught college-level courses, he never held professorial rank, and never taught an accident reconstruction course. He had enrolled in a correspondence course from the Northwestern University Traffic Institute, but had not completed the requirements for a degree or for certification by ACTAR, the Accreditation Committee for Traffic Accident Reconstruction. In addition, although he had testified in various cases, at least one court had refused to qualify him as an expert in automobile accident reconstruction because of his lack of qualifications.

    Further, the Wilson trial court noted that the expert had never conducted any studies or experiments in the field of accident reconstruction, he took no measurements and collected no data from the accident scene at issue, he failed to examine the tires or other mechanical parts of the vehicles involved in the subject accident, and he based his calculations on publicly accessible data published by the National Highway Transportation Safety Administration. Finally, the expert was unable to show that his training or experiences as a mechanical engineer gave him expertise in the field of accident reconstruction that was distinguishable from training received by other mechanical engineers. 163 F3d at 937.

    Expressing concern about the "proliferation of so-called expert witnesses" the Wilson v. Woods trial court stated: "This court personally is not convinced that there is any such thing as an accident reconstructionist as an expert field [sic]; under the rules and guidelines set forth by the Supreme Court in Daubert." Id. Continuing, the court commented upon the credentials of many accident constructionists: "None of the people who seem to be testifying have published in the field; have done experimentation in the field; and other than getting a correspondence course from this Northwestern Traffic Institute, which pads the resume, none seem to have anything other than, in most instances, a general scientific background:' Id. at 937-38. Affirming the trial court's exclusion of this expert, the Fifth Circuit concluded: "Appellee's voir dire and the court's own questioning revealed significant deficiencies in [the profferred expert's] experience and professional training, leading ineluctably to the impression that his 'expertise' in accident reconstruction was no greater than that of any other individual with a general scientific background... Because [his] claimed professional status was legitimately in doubt, the court appropriately exercised its gatekeeping responsibility┬┐ in refusing to qualify the witness." Id. at 938.

    In June 1999, shortly after the announcement of the Supreme Court's decision in Kumho Tire, the Sixth Circuit considered the admissibility of the defendant's accident reconstruction expert in Greenwell v. Boatwright, 184 E3d 492 (6th Cir. 1999). The trial court allowed defendant's expert to express an opinion regarding how the accident occurred which was different from and contradicted accident descriptions provided by several eyewitnesses. The plaintiff complained that the expert improperly testified about the credibility of eyewitness testimony and that his opinions were also unreliable because they contradicted eyewitness versions of the collision. Id. at 495,497. The Sixth Circuit analyzed the plaintiff's complaint that the opinion was unreliable under Daubert, concluding that comment by the expert on the credibility of eyewitness testimony was improper but harmless, and that the expert opinions were reliable under Daubert. The Court of Appeals affirmed the trial court's action in admitting the testimony.

    A vigorous dissenting opinion in Greenwell argued that Daubert and Kumho Tire are applied too often to the detriment of plaintiffs, and not equally against defendants.' Although these principles designed to detect and exclude junk science are perhaps most frequently applied to plaintiffs' paid experts, important that they should be applied equally to the experts of corporate defendants, as in this case. The rule is not one for plaintiff's experts only." 184 E3d at 501.

    Notably, however, although the plaintiff in Greenwell objected to the reliability of the defense expert because it contradicted eyewitness testimony, he never challenged the expert's credentials, the formulas the experience employed in his analysis, or the physical evidence upon which the expert's analysis was based, Id. at 497. Instead, plaintiff's only complaint was that the expert's opinion of how the collision occurred was not consistent with the observations of eyewitnesses. The court found that this was insufficient grounds for exclusion, concluding: "expert testimony is not inadmissible simply because it contradicts eyewitness testimony.' Id. Finding the testimony sufficiently reliable under Daubert, the court ruled that: "The plaintiffs have not proffered any basis for questioning the scientific validity of the expert's testimony, nor have they raised any issues as to its relevancy. We find that this testimony satisfies the two prong test of Daubert and was properly admitted by the district court?' Id. at 498.

    The Woods v. Wilson and Greenwell v. Boatwright opinions offer little substantive insight into how accident reconstruction testimony might be attacked on the one hand, or buttressed on the other, under Daubert and Kumho Tire. For instance, in Woods, notwithstanding the court's inherent suspicion of accident reconstruction experts, the plaintiff was obviously unprepared to meet the qualification challenge to his expert. Similarly, in Greenwell the challenging party failed to approach the matter in the terms outlined in Daubert and Kumho Tire: the basis of the objection was weak, no Daubert hearing was sought, and the focus of the objection was the expert's conclusions, not the reliability of his methodology 184 E3d at 497.

    An Exemplar Challenge

    In Smithers v. C & G Custom Hauling supra, the authors made a comprehensive attack on the reliability of the plaintiff's expert's opinion and presented expert evidence in support of that challenge at a Rule 104 (of the Federal Rules of Evidence) evidentiary hearing. Plaintiff offered a seasoned accident reconstruction expert to give an opinion as to the pre-collision speed of the defendant's vehicle. In what the authors believe to be one of the first federal court opinions post-Kumho Tire addressing the reliability of accident reconstruction testimony, the Virginia federal district court excluded the profferred testimony.

    In Smithers, the plaintiff was a passenger in a GMC truck that his fellow employee drove straight into the rear of a Peterbilt tractor and cotton hauler driven by the defendant's employee on a Virginia highway. Plaintiff's negligence theory was that despite the defendant's driver's testimony that he was traveling at approximately 40 miles per hour when he was struck in the rear by plaintiff's vehicle, the defendant was really going so slowly (seven to twelve mph) that he was an obstruction to traffic, negligently causing the collision. Since the plaintiff himself was incapable of offering testimony as to the defendant's pre-collision speed, plaintiff's counsel hired an accident reconstruction expert to offer opinions on that topic.

    The collision resulted in extensive and widespread roadway gouges and tire marks on and off the pavement. The plaintiff's ye-hide substantially "under rode" the stiff horizontal conveyor body of the defendant's truck by eleven feet, causing dramatic damage to the plaintiff's vehicle and practically shearing off the passenger cab. Both vehicles veered right after impact, out of the right westbound travel lane where the collision occurred, and into a cotton field. The off-road portion of the travel carried the defendant's vehicle through a ditch and its field side berm before the vehicles finally came to rest.

    The Expert and His Opinion(s)

    Shortly after the collision, plaintiff's expert was first hired by the plaintiff's employer's workers' compensation carrier to conduct an investigation to determine the cause and/ or causative factors of the subject traffic accident and to determine by investigation and/or traffic accident reconstruction, the causative factors and sequences of events in this crash. The expert and an assistant went to the scene of the collision on two occasions took measurements and photographs, am also inspected the plaintiff's wrecked GMC truck. Following this work the expert concluded that "the difference in the construction of the two trucks accounts for the vas differences in damage to each vehicle:' am that "there were no sight distance obstructions in the area of the crash and no back ground lighting that may have confused Mi Heath [the driver of the GMC] as he approached the scene. We know that the rear:

    lamps of the [defendant's] truck were illuminated prior to the crash. Therefore then is no explanation, short of fatigue or inattention, for Mr. Heath's failure to perceive the truck in his path?' The expert did no implicate the driver of the Peterbilt in his initial report for the workers' comp carrier which was made in March 1998.

    About a year later, after litigation was instituted by the plaintiff, the expert was hired by plaintiff's counsel. He then issued a second report in December 1999, which offered two primary opinions to support plaintiff's theory of liability- First, he indicated that the severe damage to the GMC truck occupied by the plaintiff "clearly shows" a significant speed differential between the GMC and the Peterbilt truck into which the GMC drove. Next, the expert stated that the Peterbilt was traveling at only seven to twelve mph before the impact without any warning to other vehicles, which operation amounted to a traffic hazard that" was certainly a causative factor in this crash?' The expert supported his opinion regarding pre-accident speed with typical accident reconstruction calculations, including "slide to stop" and conservation of linear momentum.

    Analyzing the Opinion

    The defendant's analysis of the plaintiff's expert's opinions and calculations led the authors to a few broad conclusions about the opinions. First, it appeared that the expert's "severe damage equals high speed differential" opinion was scientifically unsupportable. Second, the expert's calculations were flawed due to the selection of an improper scientific methodology and a substantial lack of basic accurate fact gathering measuring and testing. Finally, the expert's foundational and methodological errors led him to assert certain physical impossibilities concerning the collision. Each of the three conclusions is analyzed below.

    The expert's opinions were inconsistent, not based on adequate investigation, and not supported by accepted scientific theory

    The expert offered differing opinions de pending on who asked for the opinion. His opinion that the crush damage to the GMC truck demonstrated a significant speed differential between the vehicles contradicted his earlier opinion, which made no reference to speed differential and attributed the damage solely to vehicle structure.

    On deposition, the expert admitted that there were no published studies or tests, peer-reviewed or otherwise, that describe the speed differential necessary for the GMC to sustain the damage observed when driven into the rear of the Peterbilt truck. The expert also admitted that he could not state the speed differential necessary to result in the observed damage to the GMC. He had conducted no testing himself to determine whether his hypothesis that a ten mph differential, or any other differential, would cause the damage. The absence of scientific support for his speed differential theory punctuated the dramatic change in the expert's conclusions after the initiation of litigation. The expert had done no additional work to bolster his differential theory; he relied on the same fact investigation to prepare his December 1999 litigation report that he did for his March 1998 report.

    The expert's methodology did not fit the collision

    The methodology used by the expert was fraught with problems, and did not really apply to the particular collision at issue. The primary methodological problem was his selection of a simple" conservation of linear momentum" formula for this accident. Published literature in the field of accident reconstruction demonstrates that the conservation of momentum formula is not properly applied to rear end collisions in many circumstances.

    For example, invalid assumptions must b made to adapt the formula to some rear end collisions, such as the assumption that the two vehicles have the same post-impact departure speed. See Loumiet&Glennan7Clas-sic Errors in Accident Reconstruction: Rea Experts vs. Fakes, Fools and Frauds:' National Assoc. of Forensic Engineers (1993), at 10-11; Day, Hargens," Application and Misapplication of Computer Programs for Accident Reconstruction:' Society of Automotive Engineers, paper 89-0738 (1989), at 130; Fricke, The Traffic Accident Reconstruction Manual, Northwestern Univ. Traffic Institute (1990), at 68-6, 68-32. Post-impact departure speed here was unknown, and was just as likely not the same speed as that it was the same speed.

    Another problem with using the conservation of linear momentum formula is that the calculations are very sensitive to even small errors in data collected from the site where the post-impact travel of the vehicles is very close to straight. The collision at issue in Smithers was not collinear; rather, it was offset, which resulted in a veer to the right post-impact. Day, Hargens "An Overview of the Way EDCRASH Computes Delta-V" Society of Automotive Engineers, SAE P- 193, paper 87-0045 (1988), at 183-84. The formula also fails to shed any light on the distribution of post-impact momentum between vehicles; it merely provides that the total amount of pre-impact momentum must equal the total amount of post-impact momentum. Thus, the determination of pre- or post-impact momentum of any particular vehicle relies on the use of variables for all other values in the formula.

    Moreover, the conservation of linear momentum formula typically addresses only one collision. Yet, in Smithers, there were at least three separate collisions: (1) The extended collision between the GMC and the Peterbilt; (2) the collision between the GMC and the road resulting in an extensive pattern of gouge marks; and (3) the collision between the Peterbilt and the roadside ditch and berm.

    Thus, the expert's use of the linear momentum formula to calculate the Peterbilt's pre-impact speed was inappropriate because its application to rear-end accidents such as the one in Smithers is not generally accepted in the field of accident reconstruction. See, e.g., Daubert v. Merrell Dow Pharmaceuticals, supra, 509 U.S. at 593-95. In short, if expert's analysis did not "fit" the present collision because the expert's methodology lacked "a scientifically valid link between the sources or studies consulted and the conclusion reached:' Cavallo v. Star Enterprise, 892 E. Supp. 756, 762 (E.D.Va. 1995), aff'd in part rev'd in part sub. nom., 100 E3 1150 (4th Cir. 1996).

    The expert's calculations relied upon arbitrary variables

    The Smithers plaintiff's accident reconstruction expert failed to derive the data essential to use of the conservation of linear momeritum formula in a reliable way. In order to as sign values to the variables in the formula the expert had to perform a "slide to stop calculation, which in turn, required value for impact point, distance traveled, and co efficient of friction. The expert admitted there was no fixed impact point, and that h had merely estimated travel distances. Similarly, the expert never weighed either vehicle but relied instead on his own "reasonable estimates and registration documents ii assigning a weight for each vehicle.

    Calculated post-impact speeds, necessary for application of the linear momentum formula, were also factually unsupported. The expert never conducted any coefficient o friction testing. Instead, he arbitrarily as signed drag factors to the on-road and off road travel of the vehicles involved in the collision, without any consideration of the number of wheels present, variations in road and ground surfaces, the extent of braking by the drivers, the changes in vehicle dynamics due to the collision, and numerous other factors pertinent to the proper assessment of applicable coefficients of friction Admitting that he did no testing to deter mine the coefficients, the expert declared that his experience, education, and training allowed him to say that they were proper for a rolling vehicle. Reference, however, to published data regarding drag factors revealed that the values used by the expert were typical of tire roadway friction on smooth ice or totally unimpeded rolling. See Warner, et al, "Friction Applications in Accident Re construction' Society of Automotive Engineers, paper83-06l2 (1983),at 40-41. This expert's testimony about roadway marks gouges and skid marks made it clear that the vehicles were not rolling "unimpeded' after the collision. In sum, the expert's calculations of post-impact speeds relied not on objective findings, but rather on his own subjective estimates.

    The expert's failure to identify any published data in support of his coefficients of friction was alone enough to render his opinions unreliable and therefore inadmissible. See Kumho Tire, 526 U.S. at 157; Daubert, 509 U.S. at 593-95. The expert compounded the problem with his testimony by failing to consider the factors described above. Courts have repeatedly cited the failure to consider many of the cited variables as the basis for excluding expert testimony See, e.g.,Kale v. Douthitt, 274 E2d 476,482-83 (4th Cir. 1960) (excluding accident reconstruction testimony because the expert failed to properly factor into his coefficients of friction weights, road inclines, vehicle angles, or tire and road conditions). An even more compelling reason for the exclusion of the expert's opinion was his post-impact speed calculations, which indicated that the GMC's post-impact speed was 4.1 to 6.1 miles per hour faster than the calculated post-impact speed of the Peterbilt that it just rammed from behind. This is, of course, a physical impossibility that the expert conceded in his deposition and in his January 2000 "rebuttal" report. The expert's use of subjective values proved the truth of the axiom "garbage in, garbage out:'

    Responding to the Defense's Objections

    The defendant's expert in the Smithers litigation produced an analytical report to support the defenses objection to the admission of the plaintiff's accident reconstruction expert's opinion. In response, the plaintiff's expert produced "new" calculations to answer the problems identified with his opinions. Essentially, he offered a set of "ranging" calculations to demonstrate the reliability of his estimates of the low speed of the Peterbilt (the lead vehicle) at the moment of the rear end collision. The expert asserted that he had employed sufficiently high and low drag factors and distances to cover all likely probabilities. According to the expert, his "ranging" exercise, allegedly sanctioned by Fricke, The Traffic Accident Reconstructor Manual, reaffirmed his conclusions that the speed of the Peterbilt was very low and cause of the collision.

    In making his argument for the admissibility of the expert's opinions, plaintiff's counsel relied on three broad assertions. The firs was that the expert's education, training and experience was sufficient, based on years in the field and of testifying, to allow him to "estimate" values for otherwise measurable and quantifiable formula variables Further, the plaintiff asserted that the expert's selection of the momentum formula for this case and mode of variable derivation were justified by citations to the Fricke manual. Finally, the plaintiff asserted that the defendant was not honestly criticizing the underlying science, methodology, and reliability of the opinion but rather the expert's conclusions, with which the defendant simply disagreed.

    Plaintiff's first contention, that the expert ought to be allowed to rely on his education, training, and experience to estimate variable values, was refuted by a citation to General Electric Co. v .Joiner, 522 U.S. 136, 146(1997), where the Supreme Court stated "┬┐ nothing in either Daubert or the Federal Rules of Evidence requires a district court to admit opinion evidence which is connected to existing data only by the ipse dixit of the expert:' Plaintiff's effort to buttress his expert's methodology by arguing his qualifications was unresponsive to the defendant's attack on the reliability of the expert's methodology.

    As for plaintiff's assertion that the expert's selection of the conservation of linear momentum formula and methodology conformed to the methodologies set forth in Fricke's manual (the "bible" in the field), the authors replied to plaintiff's narrow citations with extensive references to the same work that refuted plaintiff's assertion and proved his citations to be selective and out of context. For example, plaintiff cited Fricke for the assertion that the momentum calculation was accepted in the field and fit the collision at issue in Smithers. A review of Fricke's manual revealed, however, that in rear end collisions the linear momentum calculation is often insufficient. To handle the problem presented by a rear end collision, "you need to use an energy equation along with [the conservation of linear momentum formula]" to do a proper analysis. Fricke, at 68-6. The expert had performed no energy equations or analysis.

    The expert had conducted no analysis of pre- or post-collision angles, even though it was obvious that the collision caused the vehicles to veer to the right. The Fricke manual also states, on page 68-6, that an application of the momentum formula requires the longitudinal axis of the vehicles to remain more or less collinear both before and after the collision. Given the lack of vehicular collisions the linear and post-impact direction change the expert's speed estimates were not meaningful. The defense also re-emphasized through additional citations to Fricke that errors in the approach and departure paths of the vehicles involved in the collision will result in pre-impact speed estimates which are "considerably off the mark."

    Excluding the Opinion

    The plaintiff and the defense in Smithers v. C & G Hauling clearly had differing views on the reliability, and thus admissibility, of the testimony of plaintiff's accident reconstruction expert. In response, the Virginia federal district court conducted an extensive Rule 104 Daubert hearing at which both plaintiff's and defendant's experts testified. It ultimately granted the defendant's motion to exclude the testimony offered by the plaintiff's expert.

    In its opinion, the court noted several bases for its conclusion that the proffered testimony was not reliable. It observed that the expert's change of opinion about the cause of the severe damage to the GMC (vehicle structure versus speed differential) was inadequately explained. Referring to the expert's December 1999 report as a "contradiction" of the 1998 report, the court highlighted this factor as a strong indicator of unreliability. The expert plainly gave one opinion in a non-litigation setting and another after involvement in personal injury litigation.

    The court also emphasized several aspects of the expert's calculations that made them unreliable. First, it observed that, "A valid scientific theory misapplied because of the lack of sufficient factual foundation cannot be admitted because it does not assist and, indeed, may ultimately confuse the fact finder." Smithers, at 8. The court the stated that the expert's subjective discouraging of variables "creates enough of a doubt to the overall reliability [of the opinions] render them inadmissible." Id. For example, it noted that the expert used the same drag factors for both vehicles post-impact even though the vehicles traversed pavement gravel, dirt and grass, and that he could not offer an adequate explanation for ignore the post-impact angle of departure.

    The court analyzed the expert's calculated departure speeds, and stated, "Perhaps the best example of the court's concern the reliability of the plaintiff's experts analysis is... that [the expert's methodology] results in the impossible conclusion that the plaintiff vehicle was going faster after the impact than the defendant vehicle" Id. at 9. Even though the expert tried to explain the difference in the departure speeds as in consequential because they fell "within the allowable error of his calculations," the court noted that the range of values the expert calculated for pre-collision speed was so large that it subsumed the calculated pre-impact speed for the Peterbilt. Id. at 9. This wild variability in calculated speeds was an addition indication of the opinion's unreliability.

    Summarizing the expert's testimony, the Virginia federal court stated that the expert analysis is"... best described as a patchwork of unreliable estimations blended with what is otherwise accepted science?' Id. In conclusion, the court held:"... the extent of [the expert's] assumptions, combined with h discounting of what the Court understand to be important factors for the application of the scientific principles involved and h extrapolation of various values, including the utilization of large margins of error, result in the conclusion that his proposed testimony is inadmissible under Daubert." Id. at 11, citing Daubert, 509 U.S. at 591.

    Lessons to be Learned

    Several practical lessons follow from the cases discussed in this article. First, in litigation involving accident reconstruction experts' qualifications will regularly be major issue. In Smithers v. C & G Custom Hauling, the expert's qualifications were not challenged for tactical reasons. Given, however, the expert's lack of engineering background and lack of familiarity with more complicated reconstruction methodologies, the potential clearly existed for such a challenge. The qualification problems highlight in Wilson v. Woods, supra, concerning reconstructionists with thin educational credentials, have been the subject of comment as early as 1989:

    When the opinions that need to be rendered involve vehicle and occupant dynamics and related areas, an engineering degree with a major in mechanical engineering is usually very desirable. Eye though short courses are taught in the usage of cookbook formulae for speed determination and related variables, it is impossible to impart sufficient information on the usage of these formulae to student who is usually uneducated in the areas of physics and calculus during short course. Clearly, if engineering school throughout the country are of the opinion that it takes at least four years to obtain an engineering degree and become knowledgeable in engineering principle a short course on accident reconstruction can only provide a wetting of the appetite for the participating student and not the information that will make him a qualified witness in engineering dynamics in a court of law.

    Martinez, et al.," A Primer of an Automobile Accident Reconstruction:' SAE SP-779, paper 88-90631 (1989).Also, as highlighted by the court in Wilson, 163 E3d at 937-38, lack of experience in the field can be equally troublesome.

    Beyond the qualification issue, accident reconstruction experts must demonstrate scientifically valid methodology to support their opinions. Although Kumho Tire is often viewed as a product liability case, the reliability analysis employed there provides a blue print applicable to analysis of traffic accident reconstructionists. In order to produce an liable, admissible report, reconstructionist must conduct extensive early fact gathering adopt statistical quality control processes, and follow through on the "scientific method" (which includes testing of hypotheses an their falsification).

    Although it is considered the tradition reference source for accident reconstruction Fricke's The Traffic Accident Reconstruction Manual is considerably out of date at this writing. For example, although Fricke does caution about sensitivity and has an entire section on "why reconstructions go wrong", it does not speak in terms "methodology", "hypothesis," and "falsifications." Focused approaches to implement statistically valid methods of sensitivity analysis are absent from Fricke's manual. In short, it does not "speak the language Daubert" a technique now required of all experts in litigation. See Sneed, "The Ongoing Revolution in Expert Witness Practice: Daubert in the 7th Circuit," 86 Ill. Bar J. 4l8, 423 (1998). Research from the Society of Automotive Engineers has not yet worked its way into accident reconstruction text books. The risk of misapplication of simplified reconstruction programming available off the shelf and the need for genuine sensitivity analysis to highlight such misapplications was recently noted by one observer:

    The potential for the analyst to be able t reconstruct any accident depends on the data and measurements available. All such data are subject to measurement an estimation errors. The responsible reconstructionist must accommodate a range of values for the independent variables o the problem, even if (s)he personally tool the data. It is therefore absolutely imperative to examine the sensitivity of final calculations to such variations in data.

    Various software packages are available to mechanize the calculation of speech continued on from slide to stop measurements, combining a number of tire/road coefficient of friction values, speed from yaw measurements, speeds calculated from vaults, trip, rollovers and falls, and speeds calculated using momentum balance techniques. These are often massively simplified for use by police officers with little or no engineering or physics background, and consequently are often seriously misapplied by such individuals. The use of sensitivity analyses such as those developed above quickly and clearly shed strong light on such misapplications.

    Metz et al.," Sensitivity of Accident Reconstruction Calculations," Society of Automotive Engineers, SAESP-l3l9, paper98-0375 (1998), at 347.


    In order to successfully argue the reliability of an opinion, or to oppose an accident reconstruction opinion, there must be close cooperation between the defense attorney and his or her expert to pose the scientific principles and arguments within the applicable legal framework. Reconstructionists will be called upon to consult and do research much more than in the past. Reconstructionists will be called upon to consult and do research much more than in the past. Academically qualified and field experienced reconstructionists may often find themselves called upon to serve as methodology experts, consulting solely to test the reliability the opposing expert's opinion. Indeed, in Smithers, the defense's accident reconstruction pert offered no opinion as to pre-impact speed because there was simply insufficient empirical data upon which to base such an opinion. The court apparently put more credence in the defense expert's refusal to offer an opinion as to pre-impact speed than it did to contested opinions from the plaintiff's expert. The court expressly relied upon the defense expert's criticisms of plaintiff's expert's analysis in deciding to exclude the latter.

    Accident reconstructionists who can actually" practice what they preach" will find their opinions admitted much more often than those that cannot, will not, or are not authorized to do the necessary investigative and scientific work to support their opinions. Counsel will have to learn both the law and the science to focus the court's attention on the scientific underpinnings of the legal arguments. An understanding of where the science and law merge ill support a presentation that prevents the technical terminology and accident reconstruction jargon from impairing the court's understanding of the core engineering and scientific issues crucial to a genuine reliability assessment. It will also help establish that counsel is proceeding from a position of scientific strength and not mere legal gamesmanship.