Abstract: Traffic volume and vehicle loads are increasing with time during the bridge service life. Time-dependent reliability theory considers the time-varying effects of loads and resistance, which has been commonly adopted in recent engineering reliability research. The degradation of bridge resistance and increase of vehicle load and frequency varies with time, as described by a nonstationary stochastic model. The gamma stochastic process is adopted to describe the frequency function of vehicle load occurrence to promote the application of nonstationary processes in reliability studies, and time-dependent reliability analyzing approach is proposed for reinforced concrete bridges based on increasing load frequency. The time-dependent reliability equation is modified to account for the verifying effect of historical load information on time-varying resistance by including the coefficient of variation of bridge resistance as a time-associated variable. The above two methods are then used to perform a time-dependent reliability analysis on a prefabricated prestressed concrete bridge. The results show that the structural time-dependent reliability immunes the correlativity of frequency increment of vehicle loads; the time-dependent failure probabilities within 20 to 40 years range from those obtained by proof load tests with load intensities between 31.6% and 36.4% of the initial resistance, indicating higher precision of the modified equation. When the load frequency λ is less than ten times a year, the inspecting time interval is within 35 years, and the historical load intensity is less than 29.1% of the initial resistance, the approach based on load frequency function λ(t) is available. When the load frequency exceeds 36.4% of the bridge’s initial resistance, and the annual growth rate of frequency (γ) exceeds 150%. The RC bridge structure constructed in the marine environment has a higher failure probability within 20 years; thus, extra attention must be paid as corrosion resistance of reinforcements should be enhanced during its design and construction.