Abstract: Taking the complexity of influence factors of traffic incident duration on urban expressways into consider-ation,a duration estimation model based on random forest is proposed and developed in this paper.It attempts to provide a base for a reasonable estimation of the delays resulting from traffic incidents on urban expressways.The sample data is obtained from Shanghai Urban Expressway Monitoring Center.After data is preprocessed,the distribution of traffic inci-dent duration is analyzed.The minimum error of decision trees has been calculated through OOB data error estimation.An estimation model of incident duration is then developed.This model is then verified and its overall accuracy is found to meet the requirements as a reasonable accuracy with an average error of 6 min is achieved.It is also found that its accuracy is higher for duration within the range of 7~30 min,.The model is found to be more accurate and robust than decision-tree method.