Texting while driving is a visual problem influenced by phone viewing angle and working distance in young individuals.

Purpose: To investigate the impact of smartphone viewing distance and angle on reaction times.

Design: A prospective, self-controlled, single-center study.

Methods: Participants engaged in a driving simulation facing a large screen with a simulated brake pedal. They were tasked to stop the simulation once recognizing the deceleration of upcoming traffic. Tests were conducted without distraction and with a standardized distraction simulating texting while driving (TWD). Smartphone positions varied at distances of 30 cm and 60 cm, and at angles parallel to and 30° below the road plane. Reaction times were measured from the onset of simulated closure to detection. Stopping distances were extrapolated using data from the National Highway Traffic Safety Administration.

Results: Ninety-four participants were included with a mean age of 24 ± 2.7 years. The control reaction time was 11.5 ± 4.1 s. Reaction times significantly decreased with smartphone placement at a closer distance of 30 cm parallel (17.0 ± 3.3 s) vs 60 cm parallel (15.4 ± 3.8 s), P < 0.001. A 30-degree downward placement at 30 cm (18.6 ± 4.0 s) and 60 cm (17.9 ± 3.6 s), further decreased reaction time compared to parallel phone positioning, P < 0.001. Extrapolating to stopping distances based on real-world data, smartphone distractions placed at 30 cm 30° below the dashboard had the greatest effect, resulting in a 3 times increase of stopping distance compared to the control, 1201 vs 394 ft respectively, P < 0.001.

Conclusion: TWD significantly delays reaction time in young participants. Both the distance and viewing angle of a smartphone significantly influences reaction times during driving simulations. The greatest delays are observed when the smartphone is positioned closer to the user and at a 30-degree angle which we hypothesize is due to vision blur from increased accommodation, loss of stereopsis, and fixation with the peripheral retina.