Abstract: An equivalent vehicle loading model for steel bridges is established upon actual traffic data. The normal stress influence range at the weld toe of welded joints under moving wheel loads is determined through finite element analysis. The fatigue stress response characteristics of steel bridge decks under actual vehicle loads are explored using the structural stress index. Fatigue damage of welded components under real traffic conditions is analyzed using the linear fatigue damage cumulative criterion, and compared with the prediction value based on Fatigue Vehicle Load III in Chinese standards. The impact of vehicle weight limit ratios on fatigue life is examined, and a quantitative method for fatigue load limits is proposed. The study reveals that the normal stress influence range at the top plate weld toe extends longitudinally 0.9 m and transversely 1.3 m. Compared to the Fatigue Vehicle Load III in Chinese standards, the loading correction factor for the equivalent vehicle load on the studied steel bridge is 0.41. The most unfavourable load position accounts for 78% of total fatigue damage considering the transverse distribution of vehicle loads. To achieve a 100-year service life, the 20.23% vehicle weight for the studied bridge should be limited. The analytical framework established in this study aims to provide a theoretical basis for fatigue damage control of steel bridges under heavy traffic loads and may serve as a reference for fatigue performance evaluation of steel bridges based on loading monitoring data.