Increasing the axle load and speed on existing railway lines is one of the railway industryâ€™s approach that has been taken to improve the rail transport system. In this regard, improvement in stability of railway embankments, in terms of blanket layer inclusion, as an important part of each railway infrastructure is necessary more than ever. This study investigated the feasibility of using waste steel slag in enhancing the performance of bituminous railroad blanket layers. Waste steel slag is extensively and continuously being produced as waste from many industrial processes during the manufacture of steel products. According to Mame Steel Factory, a renown, steel processing plant in Addis Ababa, on average, about 7,000-8,000 tons of steel slag is produced as waste annually by a single steel factory in Ethiopia. However, it is left piled on sites of manufacture and later deposited in landfills.rnWell-graded natural basalt rock aggregate was blended with well-graded proportions of 25%, 50%, and 75% of waste steel slag aggregate by dry weight, adopted from previous studies. Control samples of purely natural rock aggregates and purely waste steel slag were also prepared. Marshall Mix design analysis (ASTM D1559), Indirect Tensile Strength and Moisture Susceptibility (AASHTO T283) were used to evaluate the laboratory performance of modified blanket layer mixtures.rnThe minimum Marshall Stability value for modified asphalt mixtures was 34.4% above the 8000N recommended for heavy traffic load category by AREMA specifications for concrete structures and foundations (2010). Modified mixtures of 25%, 50% and 75% Waste Steel Slag Aggregate yielded higher unconditioned Indirect Tensile Strength than the unmodified mixes. Voids in Total Mix values obtained for all modified and unmodified mixtures were within AREMA (2010) requirement of 3%-5%. On average, the Tensile Strength Ratio values of both modified and unmodified mixtures were greater than the minimum 75% recommended by AREMA (2010) specifications for good performance with 25% WSSA modified mixture emerging with the highest Tensile Strength Ratio value. Although up to 100% replacement of the basalt aggregate by Waste Steel Slag Aggregate is effective, the optimal replacement percentage is 25%. Therefore, it is possible to utilize waste steel slag to enhance the performance of bituminous railroad blankets.rnKey Words: Aggregate, Bitumen, Blanket, Waste Steel Slag, Marshall mix design.