According to Público Newspaper, this hypothesis appears in a study they had access to and in the document, two more hypotheses are defined to improve the Southern Line: reducing the trip by 20 minutes at a cost of €160 million and reducing by 10 minutes costing a further €75 million.
Additionally, Infra-Estruturas de Portugal also presents the possibility of building a new line between Funcheira and Loulé, in which passengers could save between 35 and 40 minutes. In this scenario, the cost is expected to vary between €451 and €504 million.
In the study carried out in 2017, some limitations of the Southern Line are mentioned, mainly due to the fact that part of the track between Torre Vã and Tunes has been constructed along a curve which means that high speeds have to be avoided.
"These restrictions are due to the land in the area where the Algarve Mountain crosses and the restrictions during construction, which dictated a layout adjusted to the terrain, without major works of tunnels", says the organisation. For these reasons, and according to Público, one of the options to reduce the travel time between Lisbon and Faro by 30 minutes is to build a two-kilometre tunnel.