Abstract: In order to analyze the effects of side wind on the safety of vehicles traveling on the curve sections of bridges,under the combined effects of vehicle types,road conditions,vehicle speed and wind speed,the force applied to vehicles are studied to develop a limit equilibrium equation.According to the observed data from a cable-stayed bridge in China,critical wind speed is calculated at various vehicle speeds for maintaining a safe vehicle operation.Results show that as vehicle speed increases,critical wind speed increases slightly within a certain range,then descends.Such result contrasts to previous studies which commonly believe that critical wind speed decreases with increasing vehicle speed.To further study this paradox,the relationship between vehicle speed and critical wind speed is analyzed,and the distribution range of the corresponding vehicle speed is calculated when the above paradox occurs.The conclusions from this study are helpful for presenting a comprehensive understanding of the effects of side wind on vehicle safety,and to maintain a safe operation of the bridges.