Driver Response Times: The Human Factor in Accident Reconstruction

Driver Response Times: Accident Reconstruction is more than Physics

Out of the most common hazards, drivers respond the quickest to an adjacent vehicle moving over into their lane. The low eccentricity of an intruding vehicle as it moves into a driver’s field of view causes the fastest response. Comparatively, head-on collisions cause the slowest driver response. This is because of entanglement; or simply each driver waiting on the other to make the first move. Often times, people view the field of accident reconstruction as simply analyzing physical evidence, vehicle interactions, and the dynamics of vehicles during a crash. This evidence normally includes gouge marks, skid marks, and damage patterns present on the vehicle or roadway. However, an overlooked and critical piece of reconstruction relies on the driver’s ability to recognize and respond to hazards. Human factors studies how drivers react and respond to potential hazards that are encountered in daily driving.

What is human factors?

At some point in your driving life, you have likely heard that texting and driving is dangerous. On average, a texting driver responds 93% worse than a non-texting driver to any incoming hazard. The human brain cannot multi-task well; but it can switch between tasks very quickly and frequently. Redirecting attention from the roadway to a cell phone reduces the amount of incoming information available. As a result, this distraction makes it more difficult to recognize hazards. Human factors accounts for the brain’s ability to perceive incoming information, recognize the danger, and respond in an appropriate manner. These responses can include braking, swerving, release of the accelerator pedal, and other evasive actions. Failing to recognize hazards is one of the most common occurrences drivers experience in day to day driving, making it one of the leading causes of motor vehicle accidents.

Event data recorders (EDR/black box) and video analyses have given the accident reconstruction community greater insight into driver response times. However, to understand the correct driver response time, we must account for lighting, weather conditions, hazard eccentricity, driver age, and more.

When/how should you use human factors?

Human factors applies to almost every crash scenario in some capacity. On average, drivers respond to different situations in a predictable manner. Depending on the nature of the crash (rear-end, head-on, pedestrian/bicycle, etc) the driver’s ability to recognize the hazard and respond appropriately varies. More often than not, a common driver response time used is 1.5 seconds, yet this is a simplified approach that applies only to certain situations. When performing an analysis, it is important to evaluate the driver response time based on the specifics of the situation. This way, the investigator can more accurately understand what happened or what should have happened. Contrast, pattern, size, lightning and time of exposure are a few examples of scenario specific factors that influence driver response times.

Why does it matter?

Analyzing the physical evidence from an accident is key to determine the speeds, accelerations and distances associated with one or more vehicles during a collision. However, there are instances that the physical evidence does not tell the full story or is not readily available. Human factors integrates with traditional reconstruction techniques, making driver response times just as important to evaluate the cause of a collision as the physical evidence itself.