For attorneys
Human factors and accident reconstruction
Many attorneys already work with an accident reconstructionist. A human factors expert witness answers a different set of questions, about what the driver could see, notice and do.
What each discipline answers
Accident reconstruction
The physical events of the crash
- Where the vehicles were and how fast they were moving
- The sequence and timing of the collision
- Sight lines and distances at the scene
- Time and distance calculations, often using a standard perception-reaction time
Human factors
What the driver could see, notice and do
- When a hazard could be seen, and when it could be recognized as a hazard
- Whether a standard perception-reaction time fits the conditions of the crash
- Where the driver's attention was, and what a distraction changed
- What a driver could see and recognize at night
- Whether an account of “looked but failed to see” is consistent with the research
- When a driver could tell how quickly the distance to another vehicle was closing
- Whether a gap in traffic was one that drivers would typically accept
- How impairment would be expected to affect what a driver noticed and did
- Whether signs, signals and markings could be seen and understood in time, and whether the road matched what a driver would expect
Why a standard reaction time may not settle it
A reconstruction often applies a standard perception-reaction time to work out whether a driver could have avoided a crash. Perception-reaction time is not a single fixed value. It depends on conditions such as whether the event was expected, how visible the hazard was and where the driver's attention was.
A human factors analysis asks which conditions actually applied and what the published research supports for them. Depending on the facts, that can point in either direction.
When to add a human factors expert witness
- The case turns on whether a driver should have seen a hazard sooner
- The reconstruction relies on an assumed reaction time
- A driver says they looked and did not see
- A cell phone or in-vehicle device is in the record
- The crash happened at night or in poor visibility
- A sign, signal, marking or work zone is at issue
- A young or inexperienced driver was involved
- A vehicle was struck from behind while stopped or moving slowly
- A driver turned or pulled out across the path of an approaching vehicle
- Alcohol or drugs are in the record and causation is disputed
How the two work together
The two disciplines are complementary. Accident reconstruction establishes where the vehicles were and how fast they were moving. Human factors analysis starts from that work and asks what the people involved could perceive and do in the time available. The practice does not reconstruct crashes; it works from the reconstruction and the case record.
This page is general information, not legal advice or an expert opinion on any matter. See the disclaimer.
Discuss a matter
If a case already has a reconstruction and raises questions like these, a case inquiry is the first step.