# Sustainability Analysis of the M-30 Madrid Tunnels and Madrid Rio after 14 years of Service Life
## 3 Results and Discussion
Due to the new green area created and its connection with relevant tourist attractions of Madrid, such as the Royal Palace, the Cathedral, the Matadero cultural and exhibition center and the Campo del Moro Gardens, Madrid Rio has become a new tourist point of interest of the city. However, the whole potential of the infrastructure in this sense is not completely exploited, due to a lack of information offered to tourists [72]. It is also remarkable that the economic benefits for the city as a consequence of the tunnels are only dependent on the overall design of the infrastructure, as they are unaffected by the use of greener and improved materials. * Environmental requirements: from the environmental point of view, function values of the material consumption at construction time (C6, Table 1) follow a similar trend to C1 and C3 (total costs and dismantling, Tables 1 and 2). Again, it could be assumed that non-modification of the road implies that no materials are used and then the impact of this factor is zero. By contrast, the burial of the M-30 involved consumption of several building materials, especially concrete which is made up by water, cement, aggregates, chemical additions and, in the case of reinforced structures, steel [73]. The environmental impact of the extraction, production and transport of these raw materials has been evaluated as a medium impact (I9-I13, Table 2). However, this impact increases when considering greener and improved materials; for example, high-strength concrete requires low water cement/ratios and high-strength aggregates [74,75]. That means that the consumption of cement will rise and, consequently, so will its environmental impact. Equally, the use of high-strength aggregates can raise the costs and environmental impact of the exploitation and transport of these materials, with it being the least sustainable alternative from the point of view of the environmental aspects during construction. It should also be mentioned that the trend of the function value concerning the use of recycled materials is different from that explained before (I14, Table 2). Non-recycled materials were used during the construction of the old and new layout. However, the third alternative considers the use of recycled materials as greener building materials, enhancing the sustainability of this indicator (Table 2). Moreover, the use of greener and improved materials such as high-performance or self-compacting concretes, improves the durability characteristics of the infrastructure, decreasing the number and scope of maintenance operations and extending its service life [76,77]. Thus, such an alternative is the most suitable (C6, Table 2). Additionally, one of the aims of the renovation of the M-30 was to increase the capacity of the road and improve traffic flow [9]. Such improvement and the burial of the former layout were also responsible for the enhancement of environmental indicators in the area (C9, C10, Table 2). It may be observed that the emissions of noise and pollutants increased during the construction works of the M-30 (C8, Table 2). However, once the works were finished, the environmental benefits produced by the renovation of the road were easily recognized (Table 2). For example, as shown in Figure 3, before the construction of the tunnels (2006), in the district of Arganzuela(Figure 1) which is located in the south-west sector of the M-30, the noise level was above 75 dBA. By contrast, in 2011, it was generally about 60 dBA except at the entrances and exits from the tunnels, where it was higher [10]. Spanish law [70] limits the noise levels to 65 dBA in residential areas. Therefore, the score obtained with the function value will be 0 if this limit is exceeded. Considering 45 dBA as an acceptable noise level (satisfaction value 10), the function value will exhibit a decreasing concave curve, where satisfaction will drop rapidly when approaching the point of minimum satisfaction (Figure 3, [22]).