Validating an integrated workload scale for vessel traffic services: a comparative assessment with NASA-TLX

Abstract Vessel Traffic Services Operators (VTSOs) work in safety-critical environments that require constant monitoring of cognitive workload to ensure maritime safety. This study validates the Integrated Workload Scale (IWS), a real-time, color-coded tool co-developed with VTSOs for intuitive workload assessment. The reliability and construct validity of the IWS were evaluated by comparing its scores with those from the NASA Task Load Index (NASA-TLX), the Borg Rating of Perceived Exertion (RPE), and operational indicators, including task type and emergency involvement. Data were collected from 23 VTSOs (14 males, 9 females; mean age = 42 ± 9.6 years) at two Maritime Rescue Coordination Centers in Spain that jointly managed more than 15,000 vessels and 500 emergencies annually. The IWS demonstrated strong internal consistency and high convergent validity with NASA-TLX scores (ρ = 0.842, p < .001), with an average NASA-TLX workload rating of 27.14 (SD = 10.32), indicating moderate perceived task demand. Scores also correlated with task complexity and emergency activity, supporting construct validity. Although fatigue and workload are conceptually distinct, Borg RPE scores increased significantly with time on duty (ρ = 0.459, p = .008), with 72% of operators reporting higher fatigue during night shifts. Thermographic data confirmed physiological sensitivity to workload, especially during night shifts. Unlike retrospective measures, the IWS enables real-time monitoring and operational decision-making. These findings establish the IWS as a reliable and context-sensitive instrument for improving fatigue management in maritime operations.