In order to ensure the safety of engineering structures and especially those with special regimen such as the viaducts requiring careful monitoring of spatial displacements, it is necessary to find an optimal combination of criteria that are evaluated by a multi-criteria analysis to avoid major structural degradation and their effects on of the entire structure that can generate catastrophes with major losses of human lives. In this paper we will present an optimization of the estimation functions of the evaluation criteria behaviour for the time monitoring of an engineering structure. In this paper, we are analysing a structure that has 50 years and that has a vital significance for Galati city from Romania. It is a 1.3 km-long viaduct structure connecting the city of Galati with ArcelorMittal steel company. The current legislation requires a plan for permanent monitoring of displacement in order to avoid accidents that can lead to loss of human life. Thus, we will quantify and discuss the effects of the different evaluation criteria behaviour and we will choose those that maximize the user's chances of responding without departing from those values that keep their study credible. In order to obtain the results of the multicriteria analysis, three monitoring cycles with three types of instruments on more than 30 tracking points were designed and performed.