Öztürk, Z., and T. Öztürk. “Comparison of Railway Infrastructures With and Without Ballast Referring to the Istanbul Metro System”. ITU ARI Bulletin of Istanbul Technical University, vol. 54, no. 01, Jan. 2004, pp. 85-90, https://ari.itu.edu.tr/index.php/ituari/article/view/12.