An area of great interest remains the degree to which cognitive performance is effected by driving complexity. Older adults performing complex cognitive tasks in combination with different driving environments or alone do not perform as well, necessarily, as younger adults. The authors performed an experiment in which subjects, during simulated driving, performed cognitive performance tasks with four environmental complexity levels, since it is expected that older adults in the new generation will drive more frequently than their predecessors. To assess workload capacity task impact, heart rate, a physiological index, was monitored. Different cognitive tasks were performed by 17 older drivers (ages 51-66) and 18 younger drivers (ages 19-23 years), including: Multiple Interference Task (hard task), Continuous Performance Task segments (hard task), two Wechsler Memory Scale paragraphs (easy task), and a simulated conversation on a cellular telephone (easy task). An Agilent A1 Patient Monitor was used to measure heart rate and a full cab fix based simulator running STISIM Drive (TM) using a validated simulation protocol measured driving performance. Study results indicate that in a simulated driving environment, there is, apparently, a more difficult acclimation among older adults. Physiologically, compared to younger drivers over the simulation experience's course, the heart rates of older adults at the start were higher and declined only gradually. During the cognitive tasks, younger adults generally showed higher magnitude rate increases, part of differing heart rate response patterns by age group. On hard cognitive tasks, there was significantly better performance by younger drivers, while on easy cognitive tasks, there was equal performance by both older and younger adults. The authors conclude that collecting a traditional physiological measure, heart rate, provides additional differential workload impact insight on both older and younger drivers.