ABSTRACT
The underground railway systems and the underground transportation rate for urban passenger movement are expected to increase in the next years as a response to local government campaigns promoting the use of public transport to meet the established environmental and mobility requirements. For example, the local government of Barcelona (Spain) established in 2006 an urban mobility model which envisages a 30% rise of the internal public transport rate between 2006 and 2018. According to the last data available, from 2009 and 2010, the underground railway system increased a 14.3 per cent the number of metro lines, a 10 per cent the kilometers of the network, and a 5.4 per cent the underground transportation rate, accounting for the highest raising rate among the other urban transport systems in 2010 (Ajuntament de Barcelona, 2011). Moreover, in dense and large cities, underground railway systems become a preferable transportation system as it has the potential to provide efficient and large transit volume of passengers by relieving pressure from the surface, reducing noise, improving the air quality, as well as providing extra space for other kinds of public transport and green areas in the cities. In addition, underground stations have also become multifunctional underground spaces due to their potential efficient use of spaces. However, just as every coin
has two sides, the expansion of the railway system, together with the increase of facilities provided in the stations (shopping areas, restaurants and coffee shops, etc.), have transformed underground transportation systems in big energy consumers, causing significant impacts on the energy consumption at a regional scale. For example, the London Underground, identified as the single biggest consumer of electricity in London and one of the top 10 electricity consumers in the UK, has a total annual electricity consumption of over one terawatt hour (TWh) each year (LU Report, 2008; LU Report, 2009), being this amount of electricity enough to power over 250,000 households in one year. Besides the environmental impact, the increasing energy consumption is also producing an economic impact on the transportation companies due to the rising energy fares. For example, the Barcelona Metro Network (TMB) in the city of Barcelona (Spain) quantified the annual energy costs in 28 M€ in 2010, accounting for the second highest item in the annual budget.
