Across South Africa, Arrive Alive publishes regular reports on serious road traffic crashes. The objective is not sensationalism, nor speculation, but education: identifying contributory factors, exposing unsafe behaviour, and translating forensic findings into practical prevention advice. One factor appears with relentless regularity—speed.
Speed is not limited to exceeding posted limits. Both South African and U.S. road law impose a broader duty: drivers must operate at a speed reasonable and prudent under the circumstances, having regard to traffic, roadway geometry, visibility, and weather. A speed that is technically “legal” can still be unsafe—and legally indefensible.
Yet when high-profile crashes occur, public discourse often skips evidence and rushes to judgment. Social media fills with instant “experts” declaring that the driver must have been speeding. That instinctive conclusion is precisely what forensic investigation is designed to test, not assume.
To unpack why speed findings require discipline and method, we put specific questions to forensic crash investigator Stan Bezuidenhout, focusing on how speed is actually analysed.
Why Is “They Must Have Been Speeding” a Dangerous Assumption?
There are assumptions—and then there are forensic conclusions.
Vehicle damage alone can be deeply misleading. Investigators frequently encounter cases where police reports or opposing experts describe damage as “severe,” yet closer examination shows that the vehicle’s structural members—bumper carriers, longitudinal rails, or the occupant cell—remain largely intact. Plastic body panels may be obliterated while the underlying energy-absorbing structures are scarcely displaced.
Before any inference about speed can be made, an investigator must distinguish:
- cosmetic damage (plastics, trim, sheet metal), from
- structural deformation (rails, pillars, floorpan, occupant cell).
Only once the full damage profile is understood—both direct contact damage and referred or structural deformation—can speed be evaluated with any credibility.
That said, there are collisions where the damage profile is so extreme that speed becomes very difficult to exclude as a factor. In cases involving total superstructure displacement, extensive pillar deformation, wheel intrusion far from the primary contact area, and global collapse of the occupant cell, physics leaves little room for benign explanations.
In such cases, the issue is no longer whether speed played a role, but how much speed, and how it interacted with other factors such as roadway design, visibility, or vehicle compatibility.
Do Brake Marks Automatically Indicate Speeding?
Brake marks are useful—but only if understood correctly.
Traditional skid-to-stop calculations estimate speed based on the distance a vehicle skids under full braking without further impact. But this assumes:
- sustained braking,
- known surface friction,
- and wheel lock-up.
A short brake mark does not mean low speed. A vehicle travelling at extreme speed that brakes hard only moments before impact may leave minimal visible marks yet sustain catastrophic damage.
Investigators therefore evaluate:
- degree of brake application,
- wheel lock-up versus rolling,
- presence of ABS,
- vehicle weight distribution, and
- road surface friction (drag factor).
Drag factors are ideally measured on-site using calibrated devices or test vehicles with accelerometers. Where partial lock-up occurs (for example, rear-wheel lock only), different models must be applied to account for mixed braking behaviour.
Only once braking evidence, surface conditions, and vehicle systems are fully accounted for can braking evidence meaningfully inform speed analysis.
Can Speed Be Estimated from Photographs Alone?
Yes—within limits.
Photographs, if of sufficient quality and coverage, can support minimum speed estimates using established engineering principles and empirical thresholds.
Examples include:
- Modern vehicles are typically designed to withstand impacts up to ~20 km/h with minimal damage. Visible bumper damage generally exceeds this threshold.
- Airbag deployment often occurs above ~24–30 km/h, depending on vehicle design and sensor logic.
- Bonnet deformation, axle displacement, or engine movement typically suggests impacts approaching or exceeding ~60 km/h.
- Roof deformation and extensive pillar damage usually indicate higher energy impacts well above urban operating speeds.
Investigators also use long-standing “rules of thumb,” such as approximate speed increases per inch of crush—always adjusted for vehicle stiffness, design, and compatibility.
Vehicle design matters enormously. A modern Volvo, for example, incorporates boron steel reinforcements in its A-pillars. Visible deformation of these components implies exceptionally high force input. Conversely, smaller vehicles with rigid safety cells (such as the Smart Car) behave differently and require adjusted analysis models.
How Is Speed Analysed Forensically?
Professional crash analysis works backwards.
An investigator typically begins at the vehicle’s final resting position and reconstructs:
- Post-impact travel distance and dynamics (slide, rotation, rollover).
- Interaction with the collision medium (vehicle, pole, tree, wall, barrier).
- Structural deformation and crush energy, referenced against validated stiffness coefficients derived from controlled crash testing.
- Pre-impact behaviour, including braking, steering, and lane position.
These elements are combined to determine a change in velocity (Δv)—a critical metric in both injury biomechanics and liability assessment.
Importantly, modern vehicles increasingly provide electronic corroboration, including:
- airbag control module data (“black box” data),
- vehicle telemetry and tracking systems,
- tachograph charts (commercial vehicles),
- in-vehicle camera footage,
- GPS records.
When properly preserved and interpreted, these data sources can establish speed with remarkable precision.
Does Vehicle Type and Design Matter?
Absolutely.
Different manufacturers adopt different safety philosophies, sensor thresholds, structural stiffness values, and energy management strategies. Airbag deployment logic, battery isolation systems, and crumple zone behaviour vary widely.
Treating all vehicles as analytically equivalent is a fundamental error. Any speed opinion that ignores vehicle-specific design is, at best, incomplete—and at worst, indefensible.
Does Crash Type Affect Speed Analysis?
Yes. Profoundly.
- Near-perpendicular impacts may require momentum-based or 360-degree analysis models.
- Head-on and rear-end collisions behave differently and cannot be analysed with the same assumptions.
- Rollovers demand close examination of the trip mechanism, number of rolls, sliding versus tumbling phases, and energy dissipation through repeated contacts.
- Mass disparity collisions—such as a heavy truck and a small passenger car—require special handling, as the influence of the smaller vehicle on the larger one may be negligible.
These distinctions matter in court. Misapplying a model to the wrong crash type can collapse an otherwise strong case.
What About CCTV and External Video Evidence?
External video evidence has become indispensable.
Fuel stations, toll plazas, highways, shopping centres, and municipalities routinely record traffic movement. In some cases, video footage is the only reliable evidence available.
However, retention periods are often short. Locating and securing footage must therefore be a mandatory component of any at-scene investigation protocol.
Some of the most influential reconstructions in recent years—including major truck crashes—have relied heavily on third-party or in-vehicle video to establish speed, timing, and driver response.
The Bottom Line
Speed is one of the most emotionally charged—and most frequently misunderstood—factors in crash investigation. Public opinion often treats it as obvious. Forensic science treats it as provable.
In both South African and U.S. legal contexts, courts are increasingly intolerant of speculation. Speed must be demonstrated through evidence, methodology, and transparent reasoning. Anything less is opinion masquerading as expertise.
Proper speed analysis does not rush to judgment. It reconstructs reality—one verified fact at a time.
