The resilience assessment of transportation road networks has gained significant attention in recent years since the concept of community resilience was developed. Providing a universally accepted method to assess the seismic resilience of transportation road networks comprehensively remains challenging. Herein, a quantified indicator for seismic resilience assessment of transportation road networks is developed. The time-varying function of transportation road networks is proposed first. The Monte Carlo method is employed to simulate the time-varying function and the full probabilistic seismic resilience of the road networks under earthquakes, considering the uncertainty factors in the quantification process. Furthermore, a post-earthquake restoration strategy of transportation road networks based on system function sensitivity is proposed. A comparative analysis reveals that the sensitivity-based restoration strategy significantly enhances the post-earthquake restoration speed of the road networks, leading to the improvement of its seismic resilience. A case study is conducted for an urban district in Shanghai, demonstrating the effectiveness of the proposed method in evaluating the seismic resilience of the transportation network systems. The proposed quantification and optimization methods for the seismic resilience of transportation networks provide decision support for post-earthquake road access, community resource allocation, and transportation recovery strategies.