Abstract: Traditional algorithms to calculate the reliability of travel time applied in airport road network have two main problems, which are neither considering actual conditions of road network nor airport access cost of travellers.To resolve these two problems, congested-road amendment factors and cost factors are used to develop a time estimation model for travel time to an airport.A method of minimum square error sum (LSE) is proposed to validate this improved model.The road network of Nanjing airport is taken as a case study.It shows that the LSE of the improved method is 0.57 and lower than 0.03 of traditional algorithms.Therefore, the improved method is closer to actual conditions of the road network.Reliability of travel time in the road segment of Nanjing airport is predicted between 0.69 and 0.89, while that in the road network is between 0.65 and 0.78.The improved method shows that the reliability of travel time in the road network is unevenly distributed and low in the core segments.The improved method that is proposed in this paper can be used to close the gap between the traditional algorithms and actual conditions of road network.