# Sustainability Analysis of the M-30 Madrid Tunnels and Madrid Rio after 14 years of Service Life
## 3 Results and Discussion  
The values of each indicator, criterion and requirement considered for the sustainability analysis of the renovation of the south-west sector of the M-30, as well as the SI for the three alternative solutions studied, are shown in Table 2. It can be observed that the SI of the buried M-30 situation doubles the SI of the previous layout of the road. However, the SI of the buried M-30 built with new materials is only 0.5 higher than by using conventional materials. These scores may be attributed to the premise that the M-30 regeneration was designed with consideration of the environmental and socio-economic and I enhancement of the area [14; 61; 67] (Tables 1 and 2). In this sense, it may be observed that several of the indicators selected have the same value regarding the use or not of greener and high-performance materials, as they evaluated the difference between the buried and non-buried solutions (Table 2). * Economic requirements: from the economic point of view, it is noticeable that indicators based on the costs of the infrastructure, especially its renovation and dismantling, have a value contrary to the renovation of the M-30 (C1, C3, Tables 1 and 2). It could be assumed that the first solution, the non-burial of the M-30 stretch, means that the tunnels and park are not built and does not imply any construction cost. Equally, it could also be assumed that the dismantling of a surface road layout will be cheaper than the dismantling of the tunnels. By contrast, although the renovation of the layout implied several direct and indirect costs, it could be observed that the costs generated during the service life of the structure and the indirect economic benefits of the surrounding area were considerably enhanced (C4, C5, Tables 1 and 2). It should also be considered that the older an infrastructure is the more maintenance operations it will require. As the lifecycle of the structure progresses, its resistant capacity starts to decrease, as a consequence of the inevitable deterioration of the construction materials, such as the carbonation process and, among others, reinforcement corrosion. This deterioration is slower in the early years of the structure and faster when it is reaching the end of its lifecycle [68]. So when analyzing the service life of this particular infrastructure, it is clear that the first alternative (non-buried M-30) will be the most penalized, given that structures would be older and require more maintenance (to some extent, similar to those of bridges located on the same road such as the Avenida del Mediterraneo and Avenida de la Paz). Thus, given that the accident rate was remarkably higher [9],it would have demanded relevant measures to reduce such a rate and repair damage caused by vehicle collisions. Furthermore, some of the road restraint systems would have required modernization to meet the requirements included in the Spanish standards [69]. It should also be noted that as noise levels in the surroundings of the highway were higher than those accepted for urban and residential areas [10,70], installation of sound-absorbing acoustic screens would have been necessary. Concerning the construction of the tunnels with conventional or improved materials, the first option will require more maintenance than the second one (for this reason, material consumption will be higher, as well as noise production and pollution and traffic disturbances), as improved materials will have high-performance properties regarding durability and will need less maintenance. Additionally, the average price of dwellings around the M-30, considering the size and real-estate characteristics of the districts, the real-estate value between 2005 and 2015 increased by approximately 500 euros per square meter due to the improvements provided by works [71]. This increase in real-estate values is directly related to the creation of Madrid Rio which has boosted cultural and leisure activities, as well as commercial activities, in the vicinity [14,61,67].