SKOGLUND, J. Defendant appeals his jury conviction for negligent operation of a motor vehicle and the resulting sentence. He asserts that the trial court impermissibly allowed the State’s crash reconstruction expert to testify about defendant’s speed at the time of the collision because other experts in the field believe a drag sled should not be used on wet roads or grass. We affirm.
The accident reconstructionist pulled a drag sled over the road and grass surfaces where the vehicles had traveled. He used a mathematical formula to determine the “drag factor” generated by these surfaces. He incorporated the drag factors, estimated vehicle weights, post-crash travel distances, and braking estimates into other formulas to calculate the momentum required to move the vehicles from the point of impact over those surfaces to their final resting positions. Working backward from these calculations, and accounting for the energy absorbed by the crash, he concluded that defendant had been traveling 61 miles per hour when his truck struck the decedent’s car.
Reliable expert testimony is “sufficiently rooted in scientific knowledge,” that is, grounded in scientific methods and procedures rather than mere “subjective belief or unsupported speculation.” State v. Streich, 163 Vt. 331, 343, 658 A.2d 38, 47 (1995). In assessing whether an expert’s assertion is reliable, a court may be guided by the following factors: (1) whether the applicable theory or technique can be tested; (2) whether it has been subjected to peer review and publication; (3) its known or potential error rate; and (4) whether it has been generally accepted by the scientific community. Id. (citing Daubert, 509 U.S. at 593-97). These factors are not exhaustive, and a trial court has “broad discretion to determine, on a case-by-case basis, whether some or any of the factors are relevant in evaluating the reliability of expert evidence” before it. Daewoo, 2008 VT 14, ¶ 8; see also Daubert, 509 U.S. at 589 (rejecting the “general acceptance” test, once the “exclusive test for admitting expert scientific testimony,” as incompatible with the more liberal parameters of Rule 702).
This Court has emphasized in prior cases that “Daubert presents an admissibility standard only.” Id. ¶ 12 (quotation omitted). In fact, we adopted Daubert specifically to promote more liberal admission of expert evidence. Id. (citing State v. Tester, 2009 VT 3, ¶ 18, 185 Vt. 241, 968 A.2d 895); see also Daewoo, 2008 VT 14, ¶ 9 (noting this Court’s intent to “broaden[] the types of expert opinion evidence that could be considered by the jury at trial”). The central purpose of judicial gatekeeping under Rule 702 is to screen out potentially confusing or misleading “junk science” that was “propagated primarily for litigation.” Daewoo, 2008 VT 14, ¶ 8. As noted by the U.S. Supreme Court, “[v]igorous cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof are the traditional and appropriate means of attacking shaky but admissible evidence.” Daubert, 509 U.S. at 596. When faced with questionable scientific evidence, such as that which is “well-grounded but innovative,” id. at 593, a court should focus its Rule 702 inquiry “solely on principles and methodology” and rely on the party opponents to expose the weaknesses of expert conclusions. Id. at 595; see also Burgess, 2010 VT 64, ¶ 12.
The crash reconstruction expert offered a sufficiently reliable foundation for his testimony, and the trial court properly allowed the jury to hear it even though other experts in the field find the particular of methods used inaccurate. Novel use of methods is not misleading “junk science” to be categorically excluded under Rule 702. Instead, this use here qualifies as a well-reasoned but novel application of a traditionally accepted technique.
The accident reconstructionist pulled a drag sled over the road and grass surfaces where the vehicles had traveled. He used a mathematical formula to determine the “drag factor” generated by these surfaces. He incorporated the drag factors, estimated vehicle weights, post-crash travel distances, and braking estimates into other formulas to calculate the momentum required to move the vehicles from the point of impact over those surfaces to their final resting positions. Working backward from these calculations, and accounting for the energy absorbed by the crash, he concluded that defendant had been traveling 61 miles per hour when his truck struck the decedent’s car.
Reliable expert testimony is “sufficiently rooted in scientific knowledge,” that is, grounded in scientific methods and procedures rather than mere “subjective belief or unsupported speculation.” State v. Streich, 163 Vt. 331, 343, 658 A.2d 38, 47 (1995). In assessing whether an expert’s assertion is reliable, a court may be guided by the following factors: (1) whether the applicable theory or technique can be tested; (2) whether it has been subjected to peer review and publication; (3) its known or potential error rate; and (4) whether it has been generally accepted by the scientific community. Id. (citing Daubert, 509 U.S. at 593-97). These factors are not exhaustive, and a trial court has “broad discretion to determine, on a case-by-case basis, whether some or any of the factors are relevant in evaluating the reliability of expert evidence” before it. Daewoo, 2008 VT 14, ¶ 8; see also Daubert, 509 U.S. at 589 (rejecting the “general acceptance” test, once the “exclusive test for admitting expert scientific testimony,” as incompatible with the more liberal parameters of Rule 702).
This Court has emphasized in prior cases that “Daubert presents an admissibility standard only.” Id. ¶ 12 (quotation omitted). In fact, we adopted Daubert specifically to promote more liberal admission of expert evidence. Id. (citing State v. Tester, 2009 VT 3, ¶ 18, 185 Vt. 241, 968 A.2d 895); see also Daewoo, 2008 VT 14, ¶ 9 (noting this Court’s intent to “broaden[] the types of expert opinion evidence that could be considered by the jury at trial”). The central purpose of judicial gatekeeping under Rule 702 is to screen out potentially confusing or misleading “junk science” that was “propagated primarily for litigation.” Daewoo, 2008 VT 14, ¶ 8. As noted by the U.S. Supreme Court, “[v]igorous cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof are the traditional and appropriate means of attacking shaky but admissible evidence.” Daubert, 509 U.S. at 596. When faced with questionable scientific evidence, such as that which is “well-grounded but innovative,” id. at 593, a court should focus its Rule 702 inquiry “solely on principles and methodology” and rely on the party opponents to expose the weaknesses of expert conclusions. Id. at 595; see also Burgess, 2010 VT 64, ¶ 12.
The crash reconstruction expert offered a sufficiently reliable foundation for his testimony, and the trial court properly allowed the jury to hear it even though other experts in the field find the particular of methods used inaccurate. Novel use of methods is not misleading “junk science” to be categorically excluded under Rule 702. Instead, this use here qualifies as a well-reasoned but novel application of a traditionally accepted technique.
