The detection response task (DRT) and its variations provide a new tool for measuring cognitive workload in complex task environments such as driving. A number of previous investigations have clearly established the utility of the DRT for assessing cognitive demand in tasks that do not contain a visual–manual interaction component. However, the potential utility of the DRT for assessing the cognitive demand of primarily visual–manual tasks has not yet been established. Additionally, the various task demands required by the DRT have raised concerns over potential task interference. The aim of this study was to evaluate these important research needs by assessing the performance of common in-vehicle tasks using voice recognition, steering wheel controls, and the center stack touch screen. Tasks were completed both with and without the DRT. Results indicated the presence of the DRT increased task completion time but the effect was surprisingly modest. These findings should be of interest to researchers and practitioners involved in the assessment of cognitive load in complex task environments.