Recent considerable increases in traffic intensity and wheel loads are causing fatigue cracks in orthotropic steel decks in Hanshin Expressway. From results of the periodic inspection, the fatigue cracks are detected by the 142 spans in the 1347 spans of the stock of the orthotropic steel decks as of April, 2007. Under traffic loading, in particular the effect of local wheel loads, longitudinal welds between deck plate and trough are subjected to local transverse bending moments and are susceptible to fatigue cracks. The stress in trough to deck plate welds is strongly influenced by actual-working load and run location .Then, in orthotropic steel decks in Kobe route of Hanshin Expressway, measurement of the load of actual-working traffic and generating stress was performed by Bridge-Weigh-In-Motion. The paper describes fatigue failure assessment based on this measurement results.