Between 2007 and 2014, UGE, Alstom and other industrials partners developed a new concept of railways track called New Ballastless Track (NBT). The concept was validated under 10 million fatigue cycles on a real-size mock-up at UGE. A first numerical study using a non-linear model was performed to evaluate the possibility of replacing the original reinforced concrete layer of the track slab with Steel Fibre Reinforced Concrete. The objective is to simplify the NBT track’s construction and take advantage of the redistribution of mechanical stresses on a hyper-static structure. This study led to the conclusion that this replacement was very relevant. This paper is on optimizing this Fibre Reinforced Concrete (FRC) solution by using the same non-linear numerical model. It is shown that this optimization procedure leads to a significant reduction of CO2 emissions compared with the initial one.