Demand for freight to be transported by road increases in many countries, around the world. Consequently, we should determine an interval of vehicle velocities of minimal dynamic effects on a mixed bridge. For this, we describe the dynamic behavior of the type vehicle 12-b on the steel-concrete bridge by combining the model equations of bridge, apron and vehicle and propose a framework in which the overall model equations is solved using the newmark method. In this approach, a criteria of limited deformation on the mixed bridge is required from eurocode 4 to examine the vehicle velocities that lead to minimal dynamical effects. The sensitivity analysis is experimented and this provides a number of admissible velocities of the type vehicle 12-b that satisfies the requirements of our steel-concrete mixed bridge. This type of operation is of great importance in the monitoring of a bridge at the stages of its design, construction or maintenance. Monitoring is an essential step prior to any other management action, and in the context of this monitoring, the measurements represent important issues. This is particularly true for the two special surveillance actions, which are enhanced surveillance and high surveillance; in the latter case, measurements on structures even constitute an essential condition for the very existence of high-level surveillance, because they alone are capable of giving precise information in real time on the unfavorable development of a structure.