Abstract
This work used a car-following task to study how a speech-based e-mail system affects drivers' response to the periodic braking of a lead vehicle. The study included 24 drivers from the ages of 18-24 years. A baseline condition with no e-mail system was compared with a simple and a complex e-mail system in both simple and complex driving environments. Results show a 30% increase in reaction time when the speech-based system is used. Subjective workload ratings and probe questions also indicate that speech-based interaction introduces a significant cognitive load, which was highest for the complex e-mail system. This data shows that a speech-based interface is not a panacea that eliminates the potential distraction of in-vehicle computers.