A subjective one-item measure based on NASA-TLX to assess cognitive workload in driver-vehicle interaction

[Display omitted] •Elaboration of requirements for the subjective assessment of cognitive workload.•Evaluation of eleven existing subjective instruments against the requirements.•Development of a subjective one-item measure based on the NASA-TLX mental dimension.•Three experiments with a total of N = 107 participants support scale validity, statistical objectivity and reliability. This research introduces requirements for subjective instruments that assess the cognitive workload of in-vehicle information systems (IVIS) while driving. The suitability of 11 existing subjective instruments is evaluated, but none of the instruments matches all of the proposed requirements for this specific scenario. Therefore, a new subjective one-item measure is presented. The one-item measure is based on the mental dimension of the NASA Task Load Index (NASA-TLX) questionnaire. It combines the discussed requirements for IVIS research, e.g., time-efficiency and descriptiveness for non-expert participants. A series of three studies with 107 participants overall was conducted to verify the suitability of the measure. The results show that the instrument discriminates effectively and is valid between different levels of cognitive workload. The results are stable across different experimental setups and samples, and the instrument shows high sensitivity even in non-critical cognitive load levels.