Over the last two decades, travel time reliability has been increasingly used as a key performance indicator of transportation networks. Central to the assessment of travel time reliability is the estimation of the probability mass function (PMF) of total network travel time. This paper aims to present an efficient method to estimate the PMF of total network travel time using the universal generating function (UGF) method. Moreover, the paper proposes two truncation techniques to increase the computational efficiency of the UGF method. In order to assess the applicability of the method in practice, the method is tested on different networks. The results suggest that the method is computationally much more efficient than the standard crude Monte Carlo simulation technique at different confidence levels, and that it can be applied to real-world cases with a reasonable computation time.
