A human factors experiment was conducted to investigate the potential benefits of using directional auditory cues in intelligent transportation system technologies in commercial vehicles. Twelve licensed commercial vehicle operators drove a commercial truck-driving simulator and were prompted to select highway numbers on a side-task display. Prompts were presented visually or aurally. Auditory prompts were presented either diotically (both ears simultaneously) or directionally (to either the left or right ear). The search task varied in map density and timing of the prompts in relation to speed limit changes. All experimental conditions were compared to a control condition containing no secondary task. Both driving performance (lane deviation, steering wheel angle, road heading angle error, accidents, and adherence to the speed limit) and secondary task performance (accuracy and response time) measures were collected. Results showed that drivers were able to respond more quickly and accurately to the search task when directional auditory cues were used. Results also showed that driving performance degrades when display density increases and that the use of directional auditory prompts lessens this deterioration of performance for high-density conditions.