Abstract: A reliability-based analytical approach for determining the weight limits of short to medium span bridges is presented according to the right truncated distributions of live load effects. Firstly, a right truncated probability density function is derived from the original live load effect distribution specified in the current specifications. Secondly, to assume that the resistance, dead load effect and live load effect are independent of random variables, a back-calculation model for determining the weight limit coefficients is established by considering the right truncated distribution of live load effects. Thirdly, the conditional weight limit coefficients of bridges with ideal resistances are proposed by investigating the effect of mean values of live load effects on weight limit coefficients. Additionally, a sensitivity analysis is performed to further study the effect of distribution parameters and probability distribution types of live load effects. Finally, for bridges designed according to the previous bridge design specifications, the weight limits coefficients are proposed based on the design expression of the flexural member specified in specifications. The Results show that the bridge weight limits are related to the live load adopted in design, the acceptable probability of failure and the design ratios of live load to dead load, and the distribution parameters of live loads have a little effect on the final weight limits. The proposed methodology can provide a more rational truck weight limits with uniform reliability level for short to medium span beam bridges.