Assessment of the reliability of lifelines under seismic loads requires particular attention, since the proper functioning of these systems during or after a destructive earthquake is very important. The main objective of this study is to investigate the system reliability of lifeline networks subjected to earthquake loads by concentrating on highway transportation systems consisting of viaducts, bridges, roads, and highways. Seismic reliability of a structural component is determined based on the seismic capacity of the component and earthquake loads acting on it. The future earthquake threat on the components is calculated by performing a probabilistic seismic hazard analysis. Failure reasons of bridges and asphalt roads are explained and behavior of these components under earthquake loads is discussed to determine the seismic capacities of them. In this respect, the system reliability concepts are used and bounds on the seismic reliability of a system are established. A case study based on real-life data is also presented in order to illustrate the implementation of the method. (C) 2018 American Society of Civil Engineers.