Three experiments were conducted in a driving simulator to evaluate effects of in-vehicle message modality and message format on comprehension and memory for younger and older drivers. Visual icons and text messages were effective in terms of high comprehension and high memory retention over a 50-sec delay period for both older and younger drivers. Auditory icons (earcons) were unsuitable for older drivers, although younger drivers performed well using symbolic and speech in-vehicle messages. For visual only, auditory only, and auditory plus visual messages both textual and symbolic message formats were equally effective. No adverse effects of in-vehicle message presentation were found for lateral and longitudinal vehicle control. Implications of these findings for development of ATIS guidelines were discussed.