Introduction: Driving crash is one of major concerns in all countries. Mental workload reflects the level of attention resources required to meet both objec­tive and subjective performance criteria, which may be affected by task demand, external support, and past experience. Mental workload has been commonly cited as a major cause of workplace and transportation accidents. The objective of this study was assessment of mental workload and its relation with fatigue among urban bus drivers in Tehran, Iran.

Methods: In this descriptive and analytical study, the NASA-TLX workload scale and the Samn-Perelli fatigue scale were completed by 194 professional bus drivers. Descriptive statistics as well as correlation and regression analysis were performed for data processing.

Results: The total mental workload had highest correlation with the physical demand(r=0.73, p<0.001), the mental demand (r=0.68, p<0.001) and the time pressure (r=0.58, p<0.001). The total fatigue perceived by bus driver had highest correlation with the frustration level (r=0.42, p<0.001), the time pressure (r=0.24, p<0.001) and the mental workload (r=0.21, p<0.001).

Conclusion: Mental workload, physical workload and time pressure are important determinants of the total mental workload and fatigue perceived by urban bus drivers. A comprehensive intervention program, include work turnover, trip and work-rest scheduling as well as smoking cessation, was recommended to improve mental workload and fatigue.