Thirty-six drivers of both genders from three different age groups performed auditory cognitive tasks while driving an instrumented vehicle. The tasks were of two types. The first type of task was the selection of a driving route from a list presented as a recorded sound. These tasks represented the use of In-Vehicle Information Systems (IVIS). The second type of task consisted of a conversation like series of questions designed to replicate the use of a cellular telephone while driving. The IVIS tasks consisted of two levels of information density (short-term memory load) and four element types (complexity levels) including listening, interpretation, planning, and computation. The effects of age, information density, and element type on driving performance were assessed using a composite set of performance measures. Primary measures of driving performance included lateral tracking, longitudinal control and eye glances. Secondary task performance was assessed by task completion time, skipped tasks and task errors. Additionally, subjective assessment was done using a situational awareness probe question and a modified NASA-TLX question set.

Results showed that drivers demonstrated a general decrease in their ability to maintain their lateral position with increased task complexity. Additionally, speed and following distance were less stable during tasks. During tasks, drivers glanced less at their mirrors and instruments and left their lane more often than during baseline driving periods. Even during difficult tasks, drivers had high self-confidence in their awareness of surroundings.

One result of particular interest was an increase in lane deviations and headway variance coupled with increased forward eye glance durations. It is believed that this is evidence of a condition called "Cognitive Capture" in which a driver, though looking more extensively at the forward roadway, is having difficulty tracking the lead vehicle and lane position. High cognitive load is causing the driver to disregard or shed visual information to allow processing of auditory task-related information.

Another result of concern is the inability of drivers to assess their own impairment while performing in vehicle tasks. During tasks drivers demonstrated reduced scanning of mirrors and vehicle instrumentation. This clearly demonstrates reduced situational awareness. Additionally, during tasks lane tracking and headway maintenance performance decreased as well. However, during all tasks drivers assessed their workload higher than baseline driving even though they rated it near the bottom of the scale. Also, drivers perceived no decrease in their situational awareness.

The results of this study show that driving performance can be negatively impacted by even fairly simple cognitive tasks while a driver is looking at the road with their hands on the wheel. Even while viewing the road, a driver may perform an auditory task and be cognitively overloaded to the point of safety concerns. An additional concern is that drivers underestimate the degree of their cognitive load and its impact on their driving performance.