Waterford v. Sanchez, 1 CA-CV 21-0238

Background

Pre-dawn collision: Waterford, highly intoxicated (BAC .217) and positive for drugs, driving a Mustang (cruise control ~60 mph) rear-ended a TLC truck-trailer driven by Sanchez after Sanchez entered a state highway from a stop sign. Police observed no skid marks and the Mustang’s headlights were off.
Waterford suffered severe injuries (skull and neck fractures, broken ribs/femur, collapsed lung, etc.) and sued TLC and Sanchez for negligence; jury awarded $1,250,000 and apportioned fault 90% to defendants, 10% to Waterford.
Defendants sought to present two experts at trial: Joseph Manning (accident reconstruction) and Michael Kuzel (human factors) to opine that an unimpaired driver obeying the speed limit could have avoided or mitigated the collision.
Superior court excluded the experts’ testimony in limine, finding key assumptions speculative, and limited admissible plaintiff-fault evidence to headlights, seatbelt, and related issues, precluding comparative-fault arguments based on impairment/speed/airbag.
On appeal, the court held the superior court abused its gatekeeping role under Rule 702 by excluding expert opinions that were based on factual records and reliable methodologies; it concluded the exclusion was prejudicial and vacated the judgment, remanding for a new trial.

Issues

Issue	Plaintiff's Argument	Defendant's Argument	Held
Admissibility of expert testimony under Rule 702/Daubert	Waterford argued Manning and Kuzel relied on unfounded assumptions and speculative inputs, so their avoidability opinions were unreliable and irrelevant.	Defendants argued both experts applied accepted methods to the facts; any flaws go to weight, not admissibility, and cross-examination could expose weaknesses.	Court: Exclusion was erroneous — experts relied on sufficient facts and reliable methods; gatekeeping should not supplant jury’s role.
Reliability of Manning’s reconstruction (accel rate, constant accel, inclusion of 14 ft)	Manning’s .1 g accel, constant acceleration and including stop-sign-to-edge distance were legally and factually unsound, rendering timing estimates unreliable.	Manning’s choices were supported by vehicle weight, Sanchez’s 12 mph impact estimate, and accepted reconstruction practice; competing assumptions existed.	Court: Manning’s methodology was sufficiently reliable; challenges to assumptions go to weight.
Reliability of Kuzel’s human-factors analysis (PRT, friction, regression use)	Kuzel’s perception–reaction times, use of another expert’s regression, and assumed .7 friction without testing made his opinions speculative and equivocal.	Kuzel used established regression tools and reasonable friction averages; he reasonably relied on Manning’s timing and industry-standard methods.	Court: Kuzel’s methods were admissible; reliance on others’ models and averages is permissible and affect credibility, not admissibility.
Prejudice / need for new trial from excluding avoidability evidence	Waterford contended exclusion was proper and any error was harmless because other defenses remained.	Defendants said exclusion prevented them from fully presenting comparative-fault defense (impairment and speed), which could have changed fault apportionment.	Court: Erroneous exclusion was prejudicial because it blocked comparative-fault arguments that could have altered jury allocation; judgment vacated and remanded for new trial.

Key Cases Cited

Daubert v. Merrell Dow Pharms., 509 U.S. 579 (U.S. 1993) (federal gatekeeping standard for expert reliability)
Sandretto v. Payson Healthcare Mgmt., Inc., 234 Ariz. 351 (App. 2014) (Arizona adopts Daubert principles for Rule 702 review)
Bernstein, 237 Ariz. 226 (2015) (Rule 702’s admissibility threshold and division between judge and jury)
State ex rel. Montgomery v. Miller, 234 Ariz. 289 (App. 2014) (methodology need not achieve scientific certainty to be reliable)
Pipher v. Loo, 221 Ariz. 399 (App. 2009) (factual basis and data issues generally go to weight, not admissibility)
Logerquist v. McVey, 196 Ariz. 470 (2000) (expert may be cross-examined on reliance materials; jury assesses credibility)
State v. Lundstrom, 161 Ariz. 141 (1989) (experts may rely on other experts’ opinions in forming testimony)
Ryan v. San Francisco Peaks Trucking Co., Inc., 228 Ariz. 42 (App. 2011) (comparative-fault is an affirmative defense; defendant bears burden to prove plaintiff fault)