# Sustainability Analysis of the M-30 Madrid Tunnels and Madrid Rio after 14 years of Service Life
The most effective ways to reduce emissions caused by such production entail incorporating by-products or waste materials as aggregates or reducing the amount of cement used and thus substituting part of the cement with by-products such as, among others, fly ash [15; 16]. In this case, the tunnels were built by using conventional concrete. Such concrete types are those with a compression resistance of 20-30 MPa, reaching 35-45 MPa when used in pre-stressed concrete. Improved concretes are used when specific characteristics are required, such as self-compacting, high-strength, or lightweight types [17]. Considering use of improved concretes, such as the high-strength ones (compressive strength higher than 50 MPa [18]), it should be noted that dosage would differ from that of conventional concretes. These kinds of concretes use a higher amount of cement (400-500 kg/m\({}^{3}\)), lower water/cement ratio (less than 0.3), incorporate additives and additions such as superplasticizers and silica fume (in addition, the nature, type, and maximum size of the aggregates should also be carefully studied [17; 18; 19]. These concrete types can be of significant interest to improve the lifespan of the infrastructure, although they can affect to a greater extent the carbon footprint of the construction works. Moreover, the use of special concrete requires more technology and prior studies which could imply longer execution times. Hence, any assessment of the most sustainable solution should require thorough study. The method applied to estimate the sustainability of the works performed on the south-west stretches of the M-30 is the multi-criteria decision-making model named MIVES (initials in Spanish, modelo integrado de valor para una evaluacion sostenible) [18; 20; 21]. It has been well reported that the construction sector causes a significant environmental impact during material extraction and production, the building process, service life, and end of use and demolition of an infrastructure [22; 23]. Therefore, to assess the sustainability of such an infrastructure, several factors and situations should be considered. In such a way, the aforementioned multi-criteria decision-making method (MCDM) is suitable when a large number of factors is considered and, especially, when such factors are on occasions difficult to measure. Additionally, these models are also able to integrate socio-economic factors into the environmental requirements [22]. In such a way, the MIVES method includes the environmental and socio-economic impacts of the infrastructure in the analysis. With this purpose, the inputs of the method have been a result of the factors and values defined and discussed during seminars delivered by experts [24]. Therefore, to assess the impact of M-30 works, MIVES was applied both before and after renovation, considering the current conditions and the 14 years of service life of the tunnels. During the last few years, new greener and improved materials have been used in the construction sector, such as recycled aggregates and self-compacting concrete. Therefore, an additional sustainability study of the section that considers materials is also performed. Following this rationale, this research seeks to apply the MIVES method to the buried stretch of the south-west sector of the M-30 in Madrid. It is also the purpose of the paper to make a scientific analysis of several aspects that are mainly subjective and qualitative and turn them into objective and quantitative matters in order to analyze three different and possible alternatives:  
1. Non-buried M-30: in this situation, the former layout of the M-30 was considered, before the construction of the tunnels and the creation of the Madrid Rio park. 2. Buried M-30 by using conventional materials: this is the current condition of the road and, thus, the solutions to improve its environmental and socio-economic impact on the area were analyzed. 3.