Crash Causation vs Fault: How Zach Marshall Analyzes Vehicle Collisions

When attorneys bring me into a collision case, whether it’s tied to a DUI, a PI claim, or a disputed liability scenario, one of the first questions they ask is: “What’s the difference between causation and fault?”
They get used interchangeably, but in collision analysis they are not the same thing. And separating the two is often where the strongest defense or claim leverage comes from.

Here’s how I break it down.

Understanding “Causation” in Crash Analysis

Causation answers a single technical question:
What physically caused the vehicles to collide?

This is a mechanics-and-motion question, not a legal one. When I analyze causation, I’m looking directly at:

• Speed and energy transfer
• Lane position and vehicle trajectory
• Point of impact and angle of contact
• Timing between driver actions and collision
• How the vehicles moved before, during, and after the event
• Whether the crash sequence matches the reported narrative

Causation is rooted in physics and movement. It ignores blame, intent, or traffic violations, and focuses strictly on what forces and actions led to the actual impact.

Understanding “Fault”

Fault is a legal determination based on conduct.
It answers:
Who is responsible under the law?

Fault considers things like:

• Right-of-way
• Traffic rules
• Driver decisions
• Reasonableness of actions
• Impairment or distraction
• Policy and statutory requirements

Two different agencies can analyze the same crash and reach very different conclusions because fault is interpretative.Causation is not.

Why Attorneys Need These Concepts Separated

In DUI or PI matters, the prosecution or opposing insurer often blends causation and fault together:

“Defendant was impaired, therefore they caused the crash.”

That’s rarely accurate.

A driver can be:
• impaired but not the cause
• negligent but not the cause
• technically at fault but not the cause
• the cause but not at fault
• struck due to another driver’s actions, timing, or path of travel

Cases get stronger the moment these distinctions are made clear.

How Zach Marshall Performs a Collision Review

My method separates physics from conduct so attorneys can argue both cleanly.

1. Reconstructing the Movement

I break the collision into a sequence:

• Approach
• Pre-impact movement
• Point of contact
• Post-impact movement
• Final rest positions

This reveals whether the physical crash lines up with what officers, witnesses, or insurance adjusters claimed.

2. Identifying the Technical Cause

This is where I pinpoint the actual causal action: lane deviation, unsafe merge, speed differential, failure to yield, late braking, etc.
This step alone often shifts liability dramatically.

3. Evaluating the Conduct for Fault

Once causation is established, I turn to fault.
This includes:

• Driver decision-making
• Reaction time
• Visibility and expectation
• Policy violations
• Distraction or impairment
• What a “reasonable driver” would have done

This is where impairment may matter, but only if it contributed to the physical sequence.

Why This Analysis Matters in DUI Cases

In DUI collisions, prosecutors frequently anchor their argument on impairment alone.
But impairment does not automatically equal causation.

A sober driver can make a sudden unsafe move.
Traffic patterns can force a collision.
Another driver’s lane deviation can trigger the crash.
Mechanical issues can contribute.

The question isn’t “Were they impaired?”
It’s “Did impairment contribute to the crash sequence?”

Those are not the same, and attorneys win cases on that difference.

Why This Matters in PI Cases

For PI attorneys, separating causation and fault can drastically strengthen the value of a claim.
Especially in:

• Rear-end disputes
• Multi-vehicle chain collisions
• Lane-change cases
• Intersection crashes
• Low-speed injury claims
• Crashes involving commercial vehicles

A clean causation analysis is often the difference between a weak offer and a strong settlement.

Where My Work Fits in Your Case Strategy

Attorneys bring me in when they need:

• A neutral, defensible technical explanation of how the crash happened
• A breakdown that’s easy to articulate to a prosecutor, mediator, adjuster, or jury
• Support for negotiations, motions, or trial prep
• A clean separation between physics (cause) and conduct (fault)
• An expert explanation that counters assumptions tied to impairment

My role is simple:
Make your position stronger by clarifying what actually happened.