The aim of this study was to determine the ground conditions, which were the basis to determine the thickness of the “mattress” using ground penetrating radar. Project of constructed A4 motorway sector in the area of Łańcut, included technical assumptions, concerning laying of 50 centimeter layer of a broken stone “mattress”, to strengthen the foundation of the road embankment. At the stage of field implementation of the project, the broken stone was driven into the subsoil. As a result, unfavorable geotechnical conditions resulted in increased consumption of crushed stone by about 30%. Thus, an increase in the cost of highway construction occured. On the broken stone “mattress”, a layer of embankment of thickness from 1.0 to 3.0 m was laid. Verification of the increased cost of construction, required a survey of selected area ranges of “mattress”, of increased thickness.