Geotechnical assessment of the route of a tunnel is a prerequisite for safe and stable tunneling operation. Especially, when adverse geological and structural conditions are encountered, prior knowledge is of crucial importance. The twin tube three-lane motorway tunnels being driven between Istanbul and Ankara possess probably the most difficult ground conditions ever encountered from geological and tectonic viewpoints. The tunnels were designed according to general rules of New Austrian Tunneling Method (NATM). However, severe stability problems were faced during tunneling operations. Therefore, a new supporting scheme had to be used which was significantly different from the original design. A more rigid and strong support type had to be used in contrary to the original the NATM design, which proved to be inadequate. Therefore, a pilot tunnel was driven prior to full-face advance of the tunnel. This paper presents a discussion of the pilot tunnel in a critical manner stating that it would be possible to foresee the inadequacy of NATM and revise the support strategy if a pilot tunnel was opened at the beginning of the project.