<p>The effects of age and time-varying degradation on the seismic fragility of highway reinforced concrete (RC) girder bridges are considered. A total of 1,008,858 parameters recorded by eight earthquake stations were processed (Wenchuan earthquake, China). A fragility level assessment of 356 RC girder bridges on 49 highways (between 68 cities) impacted by the Wenchuan earthquake was conducted on the basis of the Chinese earthquake intensity forms and the updated earthquake hazard model. A seismic fragility function for highway RC girder bridges was established that considers age- and time-varying degradation effects. A nonlinear prediction function considering the least squares algorithm is proposed, and a bridge seismic vulnerability curve considering time-varying degradation and age effects is developed. A set of earthquake fragility curves for RC bridges considering time-varying degradation and seismic intensity measures. The traditional earthquake fragility level of bridges was updated. An optimized earthquake vulnerability index function was established. A coupled fragility membership index model considering aging and time-varying degradation effects is developed, and a fragility membership curve based on the highway RC bridge dataset between 68 cities is generated.</p>