Future of Rail | High speed rail networks spring up worldwide despite engineering challenges

High speed rail projects are rolling out at pace worldwide, bringing unique challenges that expand the frontiers of engineering.

People never used to think of railways as equivalent in complexity to something like a nuclear power station,” says Aecom global transit director Russell Jackson. “But given the scale, the number of communities impacted, environmental safety, reliability and regulatory stakeholder interfaces when we look at high speed rail projects, they really are that complicated.”

High speed rail schemes are no ordinary railways. The International Union of Railways (UIC) defines high speed rail as “infrastructure for new railway lines designed for speeds of 250km/h and above, or upgraded existing lines for speeds of up to 200km/h or even 220km/h”.


They require straighter routes than their lower speed counterparts. Key structures such as tunnels must also be able to withstand the aerodynamic pressure loads caused by trains travelling through them at speeds sometimes exceeding 300km/h.

In defiance of the challenges posed by these schemes, high speed rail rollouts are gaining momentum globally. The UIC Rail Atlas 2022 totals the length of new lines under construction across the world’s five regions last year at just over 19,700km.

Travel update

Of these, High Speed 2 (HS2) in the UK is drawing attention internationally, with plans for services running at speeds up to 360km/h between London and North West. Trains will stop at London and Birmingham initially and later at Manchester before continuing on the existing network to Scotland and elsewhere.

HS2 will be built in three phases: Phase 1, which is under construction; Phase 2a, whose enabling legislation gained Royal Assent in 2021; and Phase 2b, which is being reviewed by the government.

Budgeted at £44.6bn in 2019, Phase 1 links London and the West Midlands via 215km of track, 50km of tunnels and 16km of viaducts. Its services are expected to start running between Birmingham Curzon Street and Old Oak Common in London between 2029 and 2033 and will expand as new sections of the network are built.

With costs set at between £5.2bn and £7.2bn in 2019, the 58km Phase 2a will extend the line to Crewe in Cheshire with a target delivery date of 2030 to 2034. Phase 2b, which has no confirmed budget, is currently designed at 85km for the Western Leg from Crewe into Manchester. There are plans to extend the Eastern Leg from Phase 1 to Midland Parkway in Nottinghamshire. Its target delivery date is between 2040 and 2045.

On these massive projects, you’ve got so many components to deal with, from the stations to the railway systems like the track and the overhead line, to the tunnels

Other projects are rolling out across Europe. In France, construction of the approximately 200km long, £8.7bn LGV Bordeaux to Toulouse line is due to start in 2024, with completion planned in 2030. This will carry trains at speeds of 320km/h. It is part of the €14bn (£12bn) “Grand Projet Ferroviaire du Sud-Ouest” (GPSO) project in south west France. The GPSO will connect the high speed line between Paris and Bordeaux with the Bordeaux to Toulouse line and the Bordeaux to Dax line.

Linking France and Italy is the 270km Turin–Lyon high speed line. Of its estimated total cost of £21.5bn, £7bn has been earmarked for the cross border section, the only part of the line where work has started.

This section, the Lyon Turin project, involves construction of a 65km rail link between Susa in Piedmont, Italy and Saint-Jean-de-Maurienne in Savoy, France. Of this, 57.5km of the line will run through the Mont Cenis Base Tunnel which will be the longest rail tunnel in the world when complete in 2032. Tunnelling work is split into three contracts worth a total of £2.58bn with Eiffage, Vinci and Implenia appointed to carry out the work in 2021. 

In Italy, a £2.9bn, 178km line is also being built in Sicily connecting Palermo and Catania. This has been split into several contracts, with WeBuild-Ghella JV winning a £1.04bn contract in May and a £1.14bn contract in June.

Further north, the under-construction £13.2bn Brenner Base Tunnel, set to open in 2032, is being built beneath the Brenner Pass on the Italian/Austrian border. Its main tunnel between Innsbruck in Austria and Fortezza in Italy will be 55km to 64km long when connected to existing tunnels and will enable trains to run at 250km/h between the two countries.

In north eastern Europe, the £5bn Baltic states’ 870km Rail Baltica network, which is scheduled for completion in 2030, will connect Estonia, Latvia and Lithuania, with further connections to Finland and Poland.

In June, the European Commission awarded £55M (€64M) to develop design documentation for the first section of a 140km, high speed rail scheme between Warsaw and Łódzźin Poland. Construction is scheduled to start by early 2024.

The Czech Republic is also engaging with high speed rail. In August 2022 the design contract for the 67km, £4.6bn Prague to Lovosice high speed line was awarded to a consortium including Valbe and Mott MacDonald. Construction of this line is expected to start in 2030.  

Elsewhere, southern Turkey’s planned 286km Mersin-Adana-Gaziantep High Speed Railway will improve connectivity between key cities and Mersin, Turkey’s second largest port.

The Moroccan government recently announced plans to launch a new high speed rail project, the Maghreb Line, a 200km link between the capital Rabat and Fez.

North American governments are also developing high speed rail schemes. In the United States, the $128bn (£100bn) 1,300km California High-Speed Rail system will be built in two major phases. The 840km Phase 1 will run through the Central Valley connecting San Francisco with Los Angeles. Phase 2 will extend the route in the Central Valley north to Sacramento, and around eastern Los Angeles to San Diego via San Bernardino and Riverside.

There are also proposals in Canada for an 800km link between Quebec and Ontario, set to launch services in the mid-2030s.

In China, China Railways put more than 2,000km of high speed railway into operation in 2022. Meanwhile trains on Indonesia’s newly completed 142km Jakarta to Bandung high speed railway reached 350km/h during recent testing in July.

In Australia, a new High Speed Rail Authority to oversee the development of a network along the country’s east coast was established in June. An inaugural project is the planned 85km link between Sydney and the coastal town of Wollongong in New South Wales.

Challenges and lessons

Mott MacDonald key account director for HS2 Neil Henderson says lessons from high speed rail projects are continuously evolving. In the case of HS2, these are captured by HS2 Ltd’s Learning Legacy platform, where project participants and industry experts can upload and share knowledge.

An example of technical insights captured by the legacy is the understanding of aerodynamic impacts in high speed rail tunnels.

HS2’s tunnels have been designed with a larger cross-sectional area to reduce the impact of complex, train-induced patterns of pressure in tunnels.

As a high speed train enters a tunnel, air inside it close to the entrance, is rapidly compressed causing a pressure wave to spread along the tunnel.

Pressure waves are also generated when the tail of a train enters a tunnel and when the nose and tail exit it, causing overlapping and rebounding wave patterns. The larger tunnel cross section for HS2 tunnels mitigates these patterns.

Mott MacDonald head of discipline for railway engineering management in UK railways John Bettles cites Crossrail as a project where lessons have informed HS2. Crossrail was not a high speed rail scheme, but it was an incubator for knowledge in areas such as the use of system engineering.

Crossrail lessons

Bettles explains: “On Crossrail we learned to implement early thinking about how to bring many diverse systems into use. This included integrating the stations and the route with the track and testing everything so that we had a reliable system from opening on day one. That approach has worked well on HS2.”

Consultants including Mott MacDonald and Aecom are also building their knowledge in parametric design for high speed rail schemes.

Many high speed rail projects around the world are still grasping the nettle of how to integrate all these different challenges in an effective way

This approach uses algorithms to create reusable customisable designs, resulting in the quicker design delivery of key structures. This brings benefits because, while lower speed railways can follow land contours, high speed rail’s requirement for straighter lines increases the need for bridges, viaducts, cuttings and tunnels, adding cost and time in construction.

Jackson adds that Aecom’s experience in collaborative delivery has been critical on high speed rail schemes. In late 2022 the consultant was engaged to deliver programme management for California High-Speed Rail project. Jackson says collaborative delivery will eliminate siloed thinking across the scheme.

He adds: “On these massive projects, you’ve got so many components to deal with, from the stations to the railway systems like the track and the overhead line, to the tunnels.

“I think many high speed rail projects around the world are still grasping the nettle of how to integrate all these different challenges in an effective way and that’s tough.”

Jackson acknowledges that high speed rail schemes often encounter dramatic cost increases, but he adds: “I think the more that we do high speed rail projects, the more we are going to get better at delivering them, particularly in areas like cost estimating.”

HS2’s cost challenges frequently make the headlines. Its budget was £51.8bn in 2019, but recent estimates place the cost closer to £155bn, with the controversial decision to suspend the development of the Euston terminus station among the scheme’s cost-related casualties.

However, Arcadis account director HS2, mobility, UK and Ireland Jonathan Sharrock says long term benefits can justify the high cost of HS2 and other schemes. He concludes: “We’re talking about infrastructure that will pay back benefits to a country’s national economy over decades.” 

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