314
When focusing on the different sub-systems, the asphalt pavement had the
greatest contribution to the total GWP because the light-weight traffi c road had the
largest surface in the street profi le (6 m
2 ). Nevertheless, there are two elements that
presented the greatest room for improvement. In both scenarios, the concrete sidewalk accounted for almost 30 % of the impacts. Generally, this material is widely
applied to pedestrian sidewalks, although asphalt is also used given its low initial
cost. Thus, the elements of the paved skins contributed the most to the urban fabric
environmental profi le, due to a more intensive maintenance of these exposed areas.
However, this might depend on the traffi c density, the type of mobility and the land
use (e.g., pedestrian areas).
The second element that presented variations in the best and worst designs was
the sewer network. In this case, the lifespan (i.e., required reposition) also played an
important role: when concrete pipes (lifespan: 100 years) were included in the best
scenario, they accounted for 10 % of the impacts; in contrast, the contribution of the
sewer increased up to 23.3 % when plastic pipes were considered (lifespan: 50
years). Hence, the integration of life-cycle environmental data and service-life
planning information is essential for urban planners for identifying long-term environmentally friendly constructive solutions (Mendoza et al. 2012b ). Finally, it was
detected that the installation of subterranean pipelines had a great contribution to
the total GWP and this trend could be extrapolated to other subterranean systems
such as telecommunication and electricity networks.
Another key issue is the variation in the street configuration. This study
presented a standard street profi le, which consisted of common pipe diameters and
trench designs. Nonetheless, the population density and the confi guration of the
city might demand larger pipe diameters because of a more intensive gas and water
consumption and wastewater production. Therefore, the contribution of these
elements to the total impact of the urban skin might increase. As a result, urban
planners must focus on the possible material and installation alternatives that best
suit their case studies (Petit-Boix et al. 2014 ).
4.2 Towards Smart Grids and Self-suffi ciency
Because networks present a relevant environmental contribution to the impacts of
the street, the cities of the future should consider approaching smart grids and selfsuffi ciency. In this sense, decentralization of urban services is essential to improve
the environmental performance of cities. This approach aims to reduce the required
networks to supply services while increasing the independence of individual neighborhoods and buildings. From an environmental point of view, this would contribute
to reducing the environmental burdens of the subterranean profi le of cities. This
strategy is particularly meaningful in low-density settlements where longer networks
are installed. In the case of gas distribution, when an isolated house requires more
than 69 m of neighborhood network, the installation of individual propane tanks
becomes favorable in terms of GWP (Oliver-Solà et al. 2009a ). Furthermore, the gas
X. Gabarrell et al.
When focusing on the different sub-systems, the asphalt pavement had the
greatest contribution to the total GWP because the light-weight traffi c road had the
largest surface in the street profi le (6 m
2 ). Nevertheless, there are two elements that
presented the greatest room for improvement. In both scenarios, the concrete sidewalk accounted for almost 30 % of the impacts. Generally, this material is widely
applied to pedestrian sidewalks, although asphalt is also used given its low initial
cost. Thus, the elements of the paved skins contributed the most to the urban fabric
environmental profi le, due to a more intensive maintenance of these exposed areas.
However, this might depend on the traffi c density, the type of mobility and the land
use (e.g., pedestrian areas).
The second element that presented variations in the best and worst designs was
the sewer network. In this case, the lifespan (i.e., required reposition) also played an
important role: when concrete pipes (lifespan: 100 years) were included in the best
scenario, they accounted for 10 % of the impacts; in contrast, the contribution of the
sewer increased up to 23.3 % when plastic pipes were considered (lifespan: 50
years). Hence, the integration of life-cycle environmental data and service-life
planning information is essential for urban planners for identifying long-term environmentally friendly constructive solutions (Mendoza et al. 2012b ). Finally, it was
detected that the installation of subterranean pipelines had a great contribution to
the total GWP and this trend could be extrapolated to other subterranean systems
such as telecommunication and electricity networks.
Another key issue is the variation in the street configuration. This study
presented a standard street profi le, which consisted of common pipe diameters and
trench designs. Nonetheless, the population density and the confi guration of the
city might demand larger pipe diameters because of a more intensive gas and water
consumption and wastewater production. Therefore, the contribution of these
elements to the total impact of the urban skin might increase. As a result, urban
planners must focus on the possible material and installation alternatives that best
suit their case studies (Petit-Boix et al. 2014 ).
4.2 Towards Smart Grids and Self-suffi ciency
Because networks present a relevant environmental contribution to the impacts of
the street, the cities of the future should consider approaching smart grids and selfsuffi ciency. In this sense, decentralization of urban services is essential to improve
the environmental performance of cities. This approach aims to reduce the required
networks to supply services while increasing the independence of individual neighborhoods and buildings. From an environmental point of view, this would contribute
to reducing the environmental burdens of the subterranean profi le of cities. This
strategy is particularly meaningful in low-density settlements where longer networks
are installed. In the case of gas distribution, when an isolated house requires more
than 69 m of neighborhood network, the installation of individual propane tanks
becomes favorable in terms of GWP (Oliver-Solà et al. 2009a ). Furthermore, the gas
X. Gabarrell et al.