This master thesis will explore the subject of carbon dioxide emissions in tunnel construction. It will involve a comprehensive carbon dioxide analysis of the current soil excavation process for a metro station which is under construction in Vienna. The analysed soil excavation process can be divided into three main processes: Use of construction equipment, transport, and dumping/recycling of the soil material. The aim of this master thesis is to find possibilities of optimizing the processes and to investigate them in terms of carbon dioxide emissions. For this purpose, the ¿Nullvariante¿ of each process is determined at the beginning. The ¿Nullvariante¿ shall represent the soil excavation process as it is currently carried out. In order to be able to evaluate the extent to which the optimizations have a positive effect on emissions, the current emissions in the ¿Nullvariante¿ are determined as a first step. A comparison of the optimized variants with the ¿Nullvariante¿ then makes it possible to determine the potential of emission savings. In the first process module, which represents the excavation of the material until the moment where the transport of the material begins, the use of construction equipment with combustion engines is investigated in the ¿Nullvariante¿. In the optimized variant, the combustion engines are replaced by construction equipment with electric engines. By comparing those two variants, a statement about the potential savings can then be made. When looking at the total amount of emissions, caused by all three process modules, the use of construction equipment has the highest share on the total emissions. Replacing the combustion engines by electrical ones would cause significant savings in emissions. The second process module investigates the emissions, caused by the transport of the material. In the ¿Nullvariante¿ the transport is carried out by trucks with a diesel-combustion engine. The optimized variants are represented by a change to electrically powered trucks and transport by rail. For short transport distances, trucks with an electric engine were considered more economical. However, if long distance transports are considered in order to recycle the material, transport by rail can be a low-emission alternative to the transport via combustion or electric engine driven trucks. The third and final process module represents the dumping or recycling of the soil material. Recycling options, that were investigated are the use as a sealing layer for landfill, the utilization in brick production or the utilization in cement production. When the material is used for brick or cement production a large number of emissions can be saved due to the fact that less material will have to be mined. Furthermore, less resources of the mines will be used, and less landfill will be produced. Considering the overall system, which means the combination of all three process modules, results have shown that considerable amounts of emissions can be saved by optimizing the processes. If combustion engines were replaced by electrical ones in the process module of the construction equipment and the transport, and the material would be used for the production of bricks or cement, the recycling of the material could compensate for all the emissions generated in module one and two and in addition to that a big amount of emissions, that would be generated by the mining of the material in one of the mines, could be saved.