Many methods of measuring carbon emissions have supported the choice of developing the most environmentally friendly mode of transport which in most cases is railway transport. So far, these measurements have only considered the phases of energy operation and supply and not of infrastructure.
The construction of high-speed line infrastructure is often forgotten when calculating the carbon emissions because it is thought to generate occasional emissions resulted before the transport operations. The global operating high-speed network is 15,231-km long and 9,172 km are under construction. Under these circumstances, the infrastructure of lines is different according to the geographic region, the space allocated to the lines etc., but they have the same features as regards the project implementation, from the planning to the works necessary for the construction of lines, equipments, civil engineering.
According to a study of UIC –“Carbon Footprint of High Speed Rail”, the emissions resulted from the construction of high-speed lines (the lines LGV Mediterranée, South Europe Atlantic-Project, Beijing–Tianjin and Taipei – Kaohsiung are considered) are between 58 t and 176 t carbon dioxide/km per year. The lines benefiting from mode-rate spaces and terrain restrictions (such as in France), produce approx. 60 t carbon dioxide/km, while in case of the projects allocating large spaces (China), the emissions have a higher value (139 t – 176 t/km).
In the execution of the high-speed line infrastructure, the main factor regarding emissions consists in the number of viaducts and tunnels: the more tunnels and viaducts, the higher the emissions. For the projects with important rail embankment works, a significant percentage of emissions comes from the use of construction materials for soil stabilisation (burnt lime and cement).
In case of viaducts and bridges, 3 different types are considered: small bridges, large bridges such as viaducts and steel bridges, for the execution of which excavation works are executed and constructions materials such as steel and concrete are used. Therefore, generally, the execution of one km of viaduct requires 1,983 t steel, 32,100 m³ concrete and a volume of 26,170 m ³ of materials which need to be transported results from the excavation activity. Likewise, the execution of one km of concrete bridge of small dimension requires only 1,301 t of steel and 14,000 m³ of concrete. Taking into account the construction works, for small bridges the resulted emissions reach 68 t carbon dioxide/km/year, but for the execution of viaducts, in flat areas (such as in China), emissions amount to 115 t, and for the viaducts built over valleys, emissions reach 183 t carbon dioxide/km/year. Nevertheless, emissions vary according to the type of structures (made of concrete, reinforced concrete or steel).
Therefore, the specific design of high-speed lines is the most efficient method for protecting biodiversity, while the adaptation to environment conditions should be elaborated during the planning stage of the route in order to minimise the impact on natural areas.
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