In civil engineering, roadway structure evaluation is an important application which can be carried out by ground penetrating radar. This paper focuses on the estimation of the time delay (and so, thickness) and interface roughness of civil engineering structure, like pavements. The influence of interface roughness is taken into account in the signal model. Thus, in this paper, we propose a new method which allows to efficiently estimate the time delay and interface roughness. Contrary to [1] which proposes two methods (one to estimate time delay and another to estimate roughness), in this paper, only one method, modified MUSIC, is used to estimate the two parameters (time delay and interface roughness). The proposed method is tested on experimental data. The experimental results show the good performance of the proposed algorithm.