Forensic Engineering Expert Witness Blog

Distracted Driving: How it Affects Liability

Posted on Fri, Jan 22, 2016 @ 11:00 AM

Distraction has always affected drivers, but the addition of interactive devices like cell phones and navigation systems has raised both the opportunity for distracted driving and awareness of its perils. Although official US statistics show that only 17% of injury-causing collisions involved distraction,1 a yearlong study monitoring drivers during regular vehicle use showed that inattention (which includes distraction) was present in the three seconds before 78% of all crashes2. Based on these data, distracted driving is a big problem. 

Proving that a driver was distracted before a collision is difficult, but understanding how distraction affects driver performance can help determine whether a driver’s ability to avoid a collision was impaired by distraction.

Effects of Cognitive Distraction

Cognitive distraction, which is anything that takes a driver’s mind off the road and away from the primary task of driving, affects a driver’s visual behaviour and response time. Drivers who are cognitively distracted spend more time focused on the road ahead and less time scanning the periphery3-6. This narrowed focus is commonly called cognitive tunnel vision and can lead to missed or late detection of hazards outside of the forward field of view.

Cognitive distraction also increases response time7-8. A recent driving simulator study9 showed that response times vary with the type and location of a hazard, but in all cases cognitively distracted drivers had longer response times than undistracted drivers. Response times increased by as much as 0.4 seconds, which adds two extra car lengths to the stopping distance at 80 km/h or 50 mph.

Was a Driver Distracted?

Establishing liability based on distraction typically means proving that the driver was distracted (e.g., on their cell phone) and then showing the distraction affected the likelihood or severity of the collision. Witness evidence or phone records can establish the driver was engaged in a distracting task. Proving the distraction affected the collision is more nuanced and requires an investigator to perform a series of analytical steps. For instance, to establish that the distraction affected a driver’s ability to avoid a collision, the following steps might be needed:

  • Use the physical evidence from the collision to estimate the driver’s response time,
  • Compare the driver’s response time to the typical response times for drivers facing a similar situation, and
  • Assess whether a typical response time would have avoided the collision.

In some cases, a slow response time alone may be sufficient to show that the driver was inattentive or distracted before the collision, but this generally requires a response time significantly longer than the range for the general population.

Distractions reduce driver performance and can be partially or completely responsible for a collision and the resulting damages. Ask your collision reconstruction engineer or human factors expert if distraction played a role in your next case, and in the meantime, put away your cell phone and minimize your other distractions while driving.

  1. National Highway Traffic Safety Administration (2013). Distracted Driving 2011, DOT HS 811 737. NHTSA’s National Center for Statistics and Analysis: Washington, DC.
  2. Dingus TA et al (2006). The 100-Car Naturalistic Driving Study, Phase II – Results of the 100-Car Field Experiment, DOT HS 810 593. Virginia Tech Transportation Institute: Blacksburg, VA.
  3. Hammel KR, Fisher DL, and Pradhan AK (2002). Verbal and Spatial Loading Effects on Eye Movements in Driving Simulators: A Comparison to Real World Driving. Proceedings of the Human Factors and Ergonomics Society Annual Meeting, vol. 46, no. 26, pp. 2174–2178.
  4. Harbluk JL, Noy YI, Trbovich PL, and Eizenman M (2007). An on-road assessment of cognitive distraction: Impacts on drivers’ visual behavior and braking performance. Accident Analysis and Prevention, vol. 39, pp. 372–379.
  5. Recarte MA and Nunes LM (2000). Effects of verbal and spatial-imagery tasks on eye fixations while driving. Journal of Experimental Psychology: Applied, vol. 6, no. 1, pp. 31–43.
  6. Reimer B (2009). Impact of Cognitive Task Complexity on Drivers’ Visual Tunneling. Transportation Research Record: Journal of the Transportation Research Board, vol. 2138, pp. 13–19.
  7. Caird, J. K., Willness, C. R., Steel, P., & Scialfa, C. (2008). A meta-analysis of the effects of cell phones on driver performance. Accident Analysis & Prevention, 40(4), 1282–1293.
  8. Horrey, W. J., & Wickens, C. D. (2006). Examining the Impact of Cell Phone Conversations on Driving Using Meta-Analytic Techniques. Human Factors: The Journal of the Human Factors and Ergonomics Society, 48(1), 196–205.
  9. D’Addario P (2014). Perception-response time to emergency roadway hazards and the effect of cognitive distraction, Master of Applied Science. University of Toronto. 

Tags: Human Factors, distracted driving