Purpose: This study relied on acoustic measures of connected speech and several indices of driving performance to quantify interference between speaking and simulated driving. Method: Three groups of 20 younger (ages 20-30 years), middle-age (ages 40-50 years), and older (ages 60-71 years) adults produced monologues and completed a simulated driving task, which involved maintaining a constant speed and lane position on a freeway. Both tasks were completed separately and concurrently. Results: There were significant divided attention effects, with a reduced speaking time ratio, and increases in vocal intensity, speed variability, and steering wheel adjustments. There was a significant between-subjects age effect for intensity and fundamental frequency as the younger group had less variation with these variables compared to the other age groups across conditions. There was a significant between-subjects age effect for lane position, steering wheel position, and speed as the younger group had less variation in lane position compared to the other 2 groups, and the older group had more variation in speed and steering wheel position compared to the other 2 groups across the experimental conditions. Conclusion: These findings reveal that divided attention conditions can impact both speech and simulated driving performance. The results also shed some light on the effects of age on speech and driving tasks, although the degree of interference from divided attention did not differ by age.