AbstractWith the recent upsurge in the construction of new ballasted railway tracks and their maintenance, the high requirement of ballast and subballast materials has become an important challenge. The use of industrial by-products in the construction of railroads can be an approach for the sustainable development of railway. With an increase in steel production, the generation of steel slag is also expected to increase at an alarming rate in India. At present, the utilization of this by-product of the steel industry is marginal; however, it has an enormous potential to be used in railroad construction. Therefore an attempt has been made to use steel slag as the subballast material in the present work. The objective of this study is to assess the strength and stiffness, leaching behavior, and mineralogical characteristics of the cement-stabilized steel slag (CSS) as a subballast layer and its implications in the design methodology. A series of laboratory tests such as compressive strength, splitting tensile, flexural strength, and flexural modulus tests were carried out on the CSS with four different (1%, 3%, 5%, and 7%) cement contents. In addition, X-ray diffraction (XRD) and scanning electron microscope (SEM) were also employed to examine the mineralogical characteristics. The results suggest that cement stabilizations lead to strength and stiffness gain along with resistance to the leaching of the trace metals such as arsenic, barium, cadmium, chromium, lead, and zinc. The results show the steel slag has the potential to be used as subballast material. A step-by-step design methodology suitable for cement-stabilized steel slag as a subballast layer has been proposed by modifying the existing Association of American Railroads (AAR) method along with a practical design example.