Cover Image, Darrera
Introduction
Barcelona’s metro system is really weird. It is the only metro system in the world to use three different track gauges (distance between rails) under two operators1. Parts of the system also feel incomplete, especially in northern neighborhoods such as Sarrià and Northern Gràcia2.
The new lines, L9 and L10, are scheduled to be completed by 2027 and aim to fill the gaps of the system. They also aim to provide easier access to the airport, which has been underserved thus far.
Map of the projected path of L9 and L10, Gencat
The Basics of Metros & TBMs
Traditional metro line construction is often extremely disruptive to the surface, as it involves digging a large trench, constructing the tunnel, and then covering it back up. This method, sometimes referred to as “cut and cover”, is often cheaper than tunneling underground. However, it can be highly disruptive, requiring bus and utility rerouting and compensation for those impacted by the construction.
Diagram of Cut and Cover construction, Works in Progress
Unfortunately, in the case of Line 9, this was deemed impossible due to the dense urban areas above the line. The solution to this problem is usually to use a TBM (Tunnel Boring Machine) which operates similarly to a mole and digs out a tunnel without needing to disrupt the land above. Line 9 is unique partly in that it is dug so deep underground that it can tunnel under all pre-existing building foundations and utilities, resulting in significantly fewer complications above ground.
Diagram of a TBM, TunnelPro
Additionally, 4 out of a total of 5 TBMs in use for Line 9 were specially designed for the line’s construction because of the widely varied terrain. As Barcelona Metropolitan puts it, “[The TBMs] must bore through highly varied geology, ranging from solid rock to soft sand.”
One other challenge with TBMs, aside from their high cost3, is that they are unable to reverse direction once the tunnel is built. This is because the completed tunnel behind the machine is smaller in diameter than the cutter head, making backtracking impossible. This led to a TBM being temporarily stuck in Zona Franca during construction in 2009.
How Line 9 Is Truly Special
Line 9 tunnels are really big, being 12 meters (or approximately 39 feet) in diameter. That’s almost double the size of a typical Metro tunnel. While the larger tunnel size may seem excessive, it’s a defining feature of Line 9. The larger tunnels allow trains to run in a stacked configuration, one direction on top of the other. This space is further utilized by building the platforms within the tunnel bore itself.
Computer Graphic showing how Line 9 platforms are stacked, PEMB
This design is significant because, as RMTransit (an urbanist and public transit analyst) explains, building platforms and stations are usually the most expensive part of a metro project. TBMs are efficient, making tunnel construction relatively inexpensive compared to the high costs of building stations. This makes the challenges of station construction—cost and land use—especially important to consider.
This method of building platforms solves some of the major hurdles behind station works, as it removes the need to dig an enormous trench for constructing the station with Cut and Cover, which requires a lot of land to do properly. It is also much more effective in Barcelona’s sandy soil than using access shafts to dig the platforms rather than Cut and Cover.
Another thing to note is that the entire line is Barcelona’s first completely driverless line, improving frequency and reliability. This also makes the line easier to operate in comparison to other metro lines, and driverless technology has already been implemented in other systems such as Paris’ lines 1, 4 and 14.
The Delays and Financial Situation
The innovative approach taken on Line 9 also brings challenges, particularly as it has never been tested. This has led to significant delays and financial overruns. According to CatalanNews, the project has had an overspend of almost €5bn since 2016.
A 2020 report by the Catalan newspaper Ara states that the project is already 14 years behind schedule. Construction on the Line is now projected to be completed in 2027, although it may be delayed even further. Many of the delays are also caused by the difficult soil that Line 9 passes under.
Conclusion
Despite its challenges, Barcelona’s Line 9 represents an innovative solution to building metros in dense urban environments—particularly within a traditionally conservative industry. While imperfect, when completed, it could set a precedent for other Metro systems to learn from. While metro construction might not seem interesting, public transit is essential in cities. Line 9 demonstrates that metro construction can be done in historic, densely populated areas without surface disruption—something far more impactful than adding another lane to the highway.
Works Cited
Catalan News. “Barcelona’s L9 metro tunnel to be completed by 2027.” Catalan News, 15 June 2022, https://www.catalannews.com/society-science/item/barcelona-s-l9-metro-tunnel-to-be-completed-by-2027. Accessed 31 October 2024.
gencat. “Línies L9 i L10. Departament de Territori, Habitatge i Transició Ecològica.” Departament de Territori, 15 June 2022, https://territori.gencat.cat/ca/03_infraestructures_i_mobilitat/transport_public/metro/linies-L9-L10/index.html. Accessed 31 October 2024.
Grau Del Cerro, Xavier. “The Metro Line 9 scandal: already 14 years behind schedule and €5bn over budget.” Ara, 25 November 2020, https://en.ara.cat/misc/line-9-metro-tube-underground-barcelona-over-budget-late-audit_1_1038504.html. Accessed 31 October 2024.
Railway Technology. “Barcelona Metro Line 9.” Railway Technology, 03 October 2012, https://www.railway-technology.com/projects/barcelona-metro-line-9. Accessed 31 October 2024.
RMTransit. A Different Way to Build a Metro? | Barcelona Line 9. 11 December 2022. Youtube, https://www.youtube.com/watch?v=OqDC488awDI. Accessed 31 October 2024.
Truini, William. “The Big Dig: Barcelona’s Metro Line 9.” Barcelona Metropolitan, 30 December 2009, https://www.barcelona-metropolitan.com/features/the-big-dig-barcelonas-metro-line-9. Accessed 31 October 2024.
Wickens, Stephen. “Station to Station: Why Subway-building Costs Have Soared in the Toronto Region.” RCCAO, April 2020, https://rccao.com/research/files/RCCAO-STATION-TO-STATION-REPORT-APRIL2020.pdf. Accessed 12 November 2024.
- TBM (Transports Metropolitans de Barcelona) and FGC (Ferrocarrils de la Generalitat de Catalunya). Could also technically be counted as three if Rodalies de Catalunya is also counted, although only operating “regional” lines. ↩︎
- Stated as a potential benefit by Henning Schwarz, the director of GISA which is the company that manages all major public construction. He states that passengers “will be able to change practically at the fringes of the city” when L9 is complete. ↩︎
- During the construction of the Canada Line in Vancouver, changing from bored tunnel to cut and cover saved more than $400 million in construction costs according to an independent study by RCCAO. ↩︎