In order to investigate the crashworthiness of unban bridge piers impacted by heavy vehicles, a refined finite element model of the bridge in conjunction with vehicle was developed. The bridge model has two spans of superstructures and one bent supported by two piers. Beam and shell elements are adopted for the superstructures, while solid elements are used for the substructure. Additionally, a modified heavy vehicle model with various lengths and weights was developed. The proposed bridge model in conjunction with the vehicles was verified against the actual damage modes reported in vehicle-impacting-bridge accidents. The validity of the proposed model was also evaluated by the energy balance curve of the impacting process. Time history impact load due to the heavy vehicle with various weights was then presented. The development trend for the magnitude and location of impact load was also discussed. Numerical results show that at a fixed impact velocity the peak impact force increases with the increase of the vehicle weight. A lagging tendency of the peak crash force occurs in the heavier vehicle, and the collision center is mainly concentrated near the first contact point. A secondary collision at the rear compartment may take place for the shorter and heavier vehicle.