Environmental impacts of road traffic and route variants: An accurate way to support decision-making processes of mountain roads and tunnels in Austria

Almost 25% of the environmental impacts, based on the indicator of global greenhouse gas emissions, are caused by traffic. For designing new traffic routes and decision-making processes, it is thus essential, that integral life cycle assessments (LCA) are conducted to ensure sustainable solutions in long term and to achieve the UN Sustainable Development Goals (SDGs). This basic study examines an ecological comparison between two fictitious traffic routes. Route A reflects a typical Austrian mountain pass road with an average gradient of approximately 3 %. Route B investigates a new route variant with a tunnel (length 1,000 m), which shortens the general route distance and minimises the inclines. The LCA considers life cycle stages from raw material supply to the usage of the tunnel over an analysis period of 100 years. The results of route B are then compared with a traffic LCA, which considers the operational emissions of route A. In assessing the tunnel, the LCA incorporates the New Austrian Tunnelling Method, Austrian materials as well as typical geological conditions. To study the traffic effects, the vehicles driven in Austria were included by the current vehicle stock and were analysed in accordance to EN 17472 and EN 15804. The results (Global Warming Potential) show that the environmental impacts caused due construction, maintenance and operation of route B are lower than the operational traffic emissions of the mountain pass road. Consequently, the tunnel variant leads to general environmental savings. Hence, constructing and maintaining the tunnel gets environmentally amortised in a short period of about 10 years. Ultimately, the traffic usage counts as main emitter over the life cycle. This research illustrates the importance of integral LCAs of transport infrastructures. Within this context, integral LCA studies support decision-making processes and will provide optimal support for a future proof sustainable built environment.