Between 2007 and 2014, IFSTTAR, Alstom and other industrials partners have developed a new concept of railways track called New Ballastless Track (NBT). A first numerical study, using a non-linear model was performed to evaluate the possibility of replacement of the original reinforced concrete layer of the track slab by a steel fiber reinforced concrete, to simplify the construction of the NBT track and to 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 the optimization of this Fibres Reinforced Concrete Railway Tracks solution by using the same non-linear numerical model. It is shown that this optimization procedure should lead to reduction of CO2 emissions compared with the initial one.