The Opening Ritual at Mediation

Anyone who mediates motor vehicle cases in Ontario will recognize the pattern almost immediately. Counsel starts to deliver their opening remarks, and before the medical records, before the treatment chronology, before the plaintiff’s lived experience, the conversation often begins with the vehicles.

Photos appear on the screen. Estimates are mentioned. Someone notes the cost of repairs. Sometimes a lawyer describes the collision as “minor,” or emphasizes that the vehicles were “driveable.” On other occasions the description moves the other way when the vehicle is said to have been “written off,” implying that the damage itself proves the severity of the collision.

In many mediations, property damage becomes the opening proxy for causation. Yet the legal and scientific reality is far more complex than that. The dynamics of injury causation in motor vehicle accidents are governed by biomechanics, not body shop invoices. Understanding that distinction, and how courts may actually treat the issue, is essential for counsel presenting or defending a claim.

The Myth of the “Write-Off”

One of the more persistent misconceptions I see arise in mediation we do is when a vehicle is described as a “write-off.”

The phrase carries rhetorical power. To a layperson, it suggests catastrophic damage. But in the world of insurance adjusting, the term often means something far more mundane, namely that the cost of repair exceeded the vehicle’s economic value.

A ten-year-old vehicle with modest market value can easily become a “total loss” after what is, from a physical perspective, a relatively modest collision. Conversely, a newer vehicle with advanced crumple zones and expensive components can sustain significant structural forces while presenting relatively modest visible damage.

The classification of a vehicle as a total loss is therefore an economic decision, not a biomechanical one.

For lawyers, the distinction matters. The label “write-off” may influence perceptions at mediation or before a jury, but it does not itself prove anything about the forces transmitted to an occupant.

Why Property Damage Does Not Equal Injury

Perhaps the most commonly repeated refrain I hear in motor vehicle mediations is that “property damage does not necessarily correlate with injury.” I have heard that statement repeated so often that it risks sounding like a cliché. But it reflects a genuine scientific principle.

Modern vehicles are designed with energy-absorbing structures to manage crash forces before they reach the occupant compartment. Crashworthy design includes a strong occupant compartment and “crumple zones to absorb the force of a serious crash.”^[1] As a result, visible damage can sometimes represent energy that was successfully dissipated before reaching the occupants.

Conversely, collisions with relatively little visible deformation may still produce rapid acceleration–deceleration forces capable of affecting the cervical spine or brain^[2].

Courts have repeatedly rejected the suggestion that the severity of vehicle damage determines whether a plaintiff could have been injured in a collision. In Gordon v. Palmer (1993), 78 B.C.L.R. (2d) 236 (B.C.S.C.)^[3], the defendant argued that the minimal damage sustained in a low-speed collision made it impossible for the plaintiff to have suffered injury. Justice Thackray rejected that reasoning, observing that the proposition that little or no vehicle damage means no injury is neither a legal principle nor a medical one. Subsequent cases have echoed the same caution. In Lubick v. Mei, 2008 BCSC 555^[4], the Court emphasized that minimal vehicle damage is not “the yardstick by which to measure the extent of injuries.” The issue of causation must instead be determined on the basis of the full evidentiary record, including medical evidence and the circumstances of the individual plaintiff.

In other words, property damage evidence may assist the Court, but it does not decide the issue.

The Physics Behind Biomechanics

Biomechanical engineering attempts to answer a fundamentally technical question: what physical forces were generated during a collision, and what effect could those forces reasonably have had on the human body?

The analysis typically begins with accident reconstruction. Engineers examine the available evidence to estimate the speed change experienced by the vehicles during the collision, often expressed as “delta-V,” which represents the change in velocity resulting from the impact^[5].

Delta-V is important because the forces transmitted to occupants are generally proportional to the change in velocity experienced by the vehicle. A higher delta-V typically corresponds to greater acceleration forces acting on the occupants.

But delta-V alone does not tell the entire story.

The biomechanics of injury also depend on numerous other factors, including the direction of the impact, the angle of collision, seat design, headrest position, whether the occupant was braced or unprepared, and the physical characteristics of the individual occupant.

An oblique impact may produce rotational acceleration of the head and neck that differs dramatically from a purely rear-end collision. Side impacts may generate lateral forces that affect the spine in different ways. Even the stiffness of a vehicle’s bumper system can influence the transfer of energy during the crash.

In other words, the same delta-V can produce very different biomechanical consequences depending on the circumstances of the collision.

What Biomechanical Experts Actually Do

Biomechanical experts are frequently retained by both plaintiff and defence counsel in motor vehicle litigation. Their work often intersects with that of accident reconstruction engineers.

The reconstruction expert typically focuses on the mechanics of the collision itself including vehicle speeds, points of impact, braking, and energy transfer.

The biomechanical expert then attempts to translate those mechanical findings into human terms. Using published research, crash test data, and engineering models, the expert may estimate the accelerations experienced by the occupant’s body and compare those forces to injury tolerance thresholds reported in scientific literature.

The analysis often involves comparisons to experimental data from crash testing or volunteer studies involving controlled impacts. These studies attempt to estimate the levels of acceleration that produce various forms of tissue stress in the cervical spine.

However, such studies have limitations. Volunteer tests may be conducted under controlled conditions with healthy participants who are aware that a collision is about to occur. Real-world crashes involve unpredictable circumstances, different occupant positions, and individuals with widely varying levels of physical vulnerability.

This limitation often becomes a central issue in cross-examination.

The Limits of Biomechanical Evidence

Courts have recognized that biomechanical engineers analyze the physical forces generated in a collision rather than diagnosing injuries or determining medical causation for a particular plaintiff. Their evidence may assist the trier of fact in understanding collision mechanics, but the ultimate question of injury and causation remains grounded in the medical evidence^[6].

A biomechanical engineer can estimate the magnitude of forces involved in a collision. But the expert cannot diagnose the plaintiff, assess pain, or determine how a specific individual’s body responded to those forces.

Medical experts ultimately address those issues.

Courts must treat biomechanical evidence as informative but not determinative. The evidence may help the Court understand the mechanics of a collision, but it does not replace clinical medical evidence about the plaintiff’s actual condition.

This distinction frequently emerges in litigation involving so-called “low velocity impact” collisions, where defendants argue that the forces involved were insufficient to cause injury.

Courts have consistently rejected the proposition that minimal property damage automatically means minimal injury. The trier of fact must assess the medical evidence and the credibility of the witnesses rather than relying solely on engineering assumptions about injury tolerance.

The Jury Problem

While judges are generally comfortable navigating competing expert opinions, juries often approach the issue differently.

Jurors bring everyday intuition into the courtroom. When they see photographs of vehicles with little visible damage, the instinctive reaction may be skepticism about the severity of the alleged injuries.

Conversely, photographs of heavily damaged vehicles may create a powerful visual narrative that reinforces the plausibility of serious injury.

For that reason, counsel on both sides devote significant attention to how vehicle damage evidence is presented at trial and certainly in our mediations.

Some plaintiffs’ counsel attempt to minimize the relevance of the photographs, emphasizing the medical evidence and the unpredictability of human injury responses. Defence counsel may emphasize the physics of the collision and the absence of visible structural damage.

The tension between those narratives is not merely rhetorical. It reflects the deeper conflict between intuitive reasoning and scientific analysis.

Expert Evidence and the Court’s Gatekeeping Role

Expert evidence in Ontario is governed by well-established principles.

Before expert testimony is admitted, the Court must determine that the evidence is relevant, necessary to assist the trier of fact, and provided by a properly qualified expert who is independent and impartial.

These principles were articulated by the Supreme Court of Canada in R. v. Mohan, 1994 CanLII 80 (SCC), [1994] 2 SCR 9^[7], which established the modern framework governing the admissibility of expert evidence.

More recently, the Ontario Court of Appeal in Moore v. Getahun, 2015 ONCA 55^[8]  clarified the role of experts and the interaction between counsel and expert witnesses, confirming that experts must provide independent opinions while recognizing that consultation with counsel during report preparation is both common and permissible.

These principles are particularly important in biomechanics cases, where the scientific aura of engineering analysis can create the impression of objective certainty.

Courts must therefore scrutinize the assumptions underlying the expert’s methodology and ensure that the opinion remains within the expert’s actual area of expertise.

Where the Real Dispute Usually Lies

In practice, the central issue in many motor vehicle cases is not whether forces existed. It is whether those forces caused the plaintiff’s ongoing symptoms.

Biomechanical experts may debate the magnitude of the forces involved in the collision. But the ultimate question for the Court often becomes whether those forces caused the injuries alleged by the plaintiff.

That determination usually depends far more heavily on medical evidence, treatment records, and the credibility of the plaintiff than on engineering calculations.

Bringing Biomechanics Back to Reality

For lawyers, biomechanics should not be viewed as a mystical science capable of resolving every causation dispute.

It is simply one analytical tool among many.

Property damage evidence may be relevant, but it is not determinative. The classification of a vehicle as a “write-off” reflects economics rather than physics. Engineering analysis can estimate forces, but it cannot diagnose pain. And juries, like all human decision-makers, inevitably interpret the evidence through the lens of common experience.

Understanding these dynamics allows counsel to present biomechanical evidence more effectively, and to challenge it more intelligently when necessary.

In the end, biomechanics does not replace the fundamental task of the Court in determining whether the plaintiff was injured, and whether those injuries were caused by the collision.

The science can illuminate the pathway to that conclusion.

But it cannot decide the case on its own.