ABSTRACT: Geology forms an essential basis and the first stage in linear engineering structure projects such as highway. Äs the case presented herein,, geology takes place to complete formality in Turkish motorway projects. However, in such large engineering structure projects route selection, and geology in this selection come first Identification of the medium, in and/or on which the motorway is located has vital importance to orient the alignment and to define the components of the motorway. Geological model studies cover essentially of geology,, hydrogeology, engineering geology and geotechnics., Reliability of each model-depends, that of the former. Each phasefeeds back to increase the confidence level of former models.