The Impact of Hand-Held and Hands-Free Cell Phone Use on Driving Performance and Safety-Critical Event Risk

Abstract

This study investigated the effects of distraction from the use of three types of cell phones: (1) hand-held (HH), (2) portable handsfree (PHF), and (3) integrated hands-free (IHF). Through a naturalistic driving study (NDS), 204 drivers were continuously recorded for an average of 31 days. Only drivers who reported talking on a cell phone while driving at least once per day were recruited. A key feature was that drivers provided their cell phone records for analysis, making this the first NDS to date to combine call and text records with continuous naturalistic driving data. Results show that drivers talked on a cell phone 10.6 percent of the time the vehicle was in operation (28% of all calls and 10% of all text messages occurred while the vehicle was being operated). Talking on a cell phone, of any type, while driving was not associated with an increased safety-critical event (SCE) risk. SCEs comprised crashes, near-crashes, and crash-relevant conflicts. Visual-manual (VM) subtasks performed on an HH cell phone, however, were associated with an increased SCE risk. HH cell phone use in general was thus found to be associated with an increased SCE risk. In contrast, PHF and IHF cell phone use, absent of any VM HH cell phone subtasks, were not found to be associated with an increased SCE risk. However, VM HH cell phone subtasks were frequently observed during hands-free cell phone use. Driver performance when using a cell phone was also investigated through a within-subject comparison. VM HH cell phone subtasks were found to significantly increase the percentage of time drivers took their eyes off the forward roadway, while talking on an HH cell phone significantly decreased the percentage of time drivers took their eyes off the forward roadway. The effects of cell phone use on vehicle control were less pronounced.

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