Abstract: A three-time estimation method based on cloud theory was presented to assess travel time reliability of urban road network under random and fuzzy conditions. The backward cloud algorithm without certain degree information was amended. Link travel time was assumed to follow the Beta distribution,and its unimodal point was m and the endpoints were a and b. Based on the assumption,shape parameters were estimated. Expected value,variance,and hyper entropy of link travel time were then computed through the proposed method. In addition,digital characters of route travel time were obtained,and according to that,the routes were ranked,and route,OD and road network travel time reliabilities were provided. At last,a numerical example suggests the effectiveness of the proposed method. Therefore,the three-time estimation method combining the cloud theory can effectively solve the problem of travel time reliability under uncertainty conditions and provide reference and technical support for the urban traffic planning and management.