RAIL has long been at the forefront of the conversation about how transport, and the wider economy, can be decarbonised. With an exemplar record of low emissions compared with other modes such as road and air, rail is ideally suited as the preferred mode for a net-zero future.
But while train operations can become carbon neutral through electrification and alternative traction such as batteries or hydrogen, the scale of network expansion required to meet growing demand will inevitably have an environmental impact. The challenge is to reduce this as much as possible, to minimise the contribution to climate change.
Steel and concrete will likely remain the dominant construction materials as they are easy to maintain, robust, resilient, and last for a significant amount of time. However, the rail industry and the wider construction sector are exploring how they can deliver these same benefits with different materials and techniques.
The first step to reducing the environmental impact of constructing a new line or station is to step back and decide whether something new is needed or whether existing capacity or infrastructure can be better used, explains Mr Bas Bollinger, global leader rail and transit at Arcadis.
“Everything that you can avoid, you don’t need to reduce,” he says. “For instance, ERTMS does not only help interoperability, but also increases the efficient use of existing capacity. You can do data-lead analysis on the existing assets… because then you can avoid or reduce not only the materials, but also the activities of any kind. So that’s the bigger picture we all always need to keep in mind before we drill down to construction itself.”
Bollinger says identifying the major sources of emissions is also important when selecting solutions with the greatest impact.
“If you have relatively low capital investment, but you’re like the Class 1s in the US where 90% of your emissions are diesel, you can still focus on the 10%, but you can really make an impact if you find a solution for diesel,” he says.
The biggest shifts to reduce carbon and environmental impacts are being made in the planning stages well before a spade is even put in the ground. The early engagement of a carbon lead is important, says Aecom senior director, sustainability, Ms Annika Moman, with the company developing the ScopeX system to reduce the carbon impact by making smarter design choices.
“By understanding and quantifying the carbon implicit in these designs, we can identify the optimum combination of location, situation, site, logistics, materials, construction methods and in-use operations to minimise energy use, optimise sources of renewable power and integrate nature-based solutions wherever feasible,” Moman says.
“While there are many opportunities to reduce emissions through careful and considered design choices, the emissions resulting from the asset’s construction and delivery, and its future operation, can be substantial. The impact of these emissions can be reduced and methods to support net carbon neutral goals can be introduced where a holistic approach is taken across the life cycle, considering elements such as the use of low carbon materials, low and renewable energy, nature-based solutions - for example providing new vegetation alongside rail lines - and looking at how redundant materials can re-enter the circular economy.”
Nairobi Central Station (see panel below) is one such project being designed with sustainability at its core.
“The Nairobi project was driven by sustainability goals,” says Mr Chris Crombie, design director at Atkins, an SNC-Lavalin subsidiary which produced the station design. “When we were given the brief from Kenya Railways, front and centre was ‘we want this to be a sustainable exemplar of how to change the way stations are delivered’.”
Crombie says that station design usually begins with the overall design before sustainability is considered as an addition, rather than a central pillar.
“When we were given the brief from Kenya Railways, front and centre was ‘we want this to be a sustainable exemplar of how to change the way stations are delivered’.”Chris Crombie
“Stations are approached as an engineering challenge more than anything else, in which case it’s a problem to be solved efficiently and effectively,” he says. “But very often, that ends up with a singular solution, which only has just one answer. What we’ve done here is we’ve tried to think about what the ambitions of the project are, not just the needs of the railway, and then come to a conclusion which satisfies both, rather than just forcing us to retrofit things onto a solution that was right for the railway.”
A major innovation with the Nairobi project is the building’s water capture system, important in a region that can experience extremes of low and high rainfall, causing both drought and flooding.
Instead of being piped away, the water is directed down the spokes on the fan-shaped roof before creating a waterfall effect as it drops into a garden bed on the ground, where it can be collected and used to water the gardens or for the station’s toilets.
“You can imagine during rainfall there would be 14 of these waterfalls all shooting off in different directions from the roof and being collected within these big feet on the ground,” Crombie says. “The station had this ambition that it wanted to be environmentally sustainable, it wanted to do the right thing for the city. And we want people to be aware of that, so rather than conceal it with pipes and hide it behind walls, we actually wanted to make a feature of it.”
Parts of the large public area in front of the station are also designed to flood, absorbing water like a sponge before allowing it to be evaporated or dissipated naturally.
The building will be covered with around 11,000m² of photovoltaic solar panels, which will provide enough energy to operate the station, making it self-sufficient. This will be supported through natural rather than mechanical ventilation, further reducing energy needs.
“Rather than force air in or introduce air-conditioning, which of course has operational costs and also a really high carbon impact, we looked at a stack ventilation approach by separating all the various layers of the building, so the large, rippled roof that sits around the public space is lifted off the concourse building in the centre,” Crombie says. This allows the hot air at the top of the building to escape, drawing cooler air in from the open areas below and creating a natural ventilation stack effect. “We no longer have to cool the building artificially, which is a huge saving in terms of the operational costs, but also the carbon footprint of the station itself.”
Atkins was encouraged to incorporate landscaping into the building’s structure to represent the abundance of nature that surrounds the city. The design team took this idea a step further and looked at ways plants within the building could become functional.
“We’ve designed the centre of the building as what we call the green heart, a planted space with the principle of trying to scrub the air within the centre of the building,” Crombie says. “As you can imagine, in a station this size there is going to be a lot of brake dust and other things floating around. But introducing the right plants in the right place with the right purpose can actually help clean the air and reduce the amount of particulates that are floating around.”
Nairobi Central Station project creates “new city centre”
THE Nairobi Railway City and Central Station Project is a flagship initiative to redevelop 172ha of central Nairobi that was previously used by rail, including sidings and yards.
The British and Kenyan governments unveiled the final design of the new station and surrounding public area, which has been developed as part of the Nairobi Railway City redevelopment programme, at the end of May. The design was developed by Atkins and submitted to Kenya Railways and the Ministry of Transport.
“The amount of space that the master plans cover is significant, it’s almost like a new city centre that’s being proposed,” Crombie says.
The city itself was largely built around the railway, and the new station is being designed as the centrepiece of a large commuter rail network, with capacity to accommodate up to 30,000 passengers per hour at peak times.
Atkins and Arup were invited to peer review an earlier Korean plan for the station, which had included lowering the station tracks. This idea was removed from the updated plans, and both contractors were invited to submit updated proposals for the new station, with Atkins selected to take its design forward.
The new design takes inspiration from the round houses synonymous with the Kenyan landscape, with a large circular roof over a space intended to be open to the public, featuring retail outlets and other amenities.
The three existing platforms will be joined by six additional passenger platforms and four dedicated freight lines. Two platform bridges will be built, with one for passengers entering the station and one for passengers exiting.
Atkins says the station is designed to be delivered in stages, with the first stage on the northern side of the railway and a subsequent second facility added on the southern side. A planning application for the first stage is expected to be submitted within the next two to three months, while the complete design should be completed in the second quarter of 2023, when the project will be ready to go out to tender.
The station also features a bus rapid transit station, to improve interchange between modes, while the area in front of the station is designed to enhance walking and cycling connections, “all the things that you would expect in a modern multimodal transport hub, but are not necessarily normal within Nairobi at the moment,” Crombie says.
The project covered by the Atkins design includes the station and a 5ha “public realm” to the north which acts as an entrance to the city from the station.
The station itself comprises four sections: a fan-shaped entrance, the ticket area and concourse, the platforms, and a smaller exit building.
“[The entrance] is very much an open building, there are no walls, no doors, no physical segregation between the outside and inside,” Crombie says. “In African culture, the circle is defined as a safe space for people to meet, because there is no front and back, everybody’s equal within a circle.
“The station allows people to walk through and get the shelter of the roof without needing to buy a ticket. You can go in and meet people to have a coffee, even if you’re not travelling by train, and that was a key objective of our approach.
“The idea is the ground level is public. You then climb up some stairs and the ticketed function of the station is within the upper level. Off to the side is the existing station building, which we’ve retained because it’s a national heritage building, so we’re reusing that as a restaurant, cafe and retail outlet.
“We’ve developed a one way in and one way out system, because the numbers that we were given to accommodate within the station were up to 30,000 passengers an hour, which is more than King’s Cross station [in London].”
In order to ensure sustainability remains front and centre during the design of a project, experts in various fields become more involved from an early stage, says Ms Marjolijn Versteegden, global solutions director, net zero facilities and sustainable communities with Arcadis. Digital techniques such as digital twins are also playing a more important role. These applications are able to simulate the effects of flooding or drought on a project, as well as indicate where heat stress might cause issues. This can allow different design factors to be tested and taken into account before a design is finalised.
“We can calculate the energy use and the carbon of the materials to see which design is the best for the client, depending on what the criteria they are looking for and if it is about risk, money and carbon footprint.”
Recycling is becoming more popular, with materials from old structures incorporated into new projects where possible.
“We talk a lot about circular materials for track, viaducts and bridges,” Versteegden says. “Many companies save materials so that you can reuse them.”
However, this can pose challenges as it can be difficult to ensure the materials envisaged in the design are available during the construction phase, with flexibility required if they are not available.
It is also important to remember that the most sustainable construction material does not always produce the most sustainable outcome. While wood was explored as a structural material for Nairobi, Atkins eventually decided on steel for the main structure.
“There’s a balance between making something that’s perceived to be sustainable, and something that’s actually efficient,” Crombie says. “There’s a material benefit in using timber because it’s sustainable, but there’s an efficiency benefit to using steel because you can use less of it.”
The structure does make use of local materials and expertise, with the roof to be covered with clay tiles. “We’ve designed it such a way so that it’s a very simple, traditional roof structure that can be crafted by skilled local craftsmen, from materials and products that are available locally,” Crombie says. “We’re not coming along with this fancy roof, this is designed to be built and delivered locally.”
The move towards sustainable practices, such as the use of electrical construction machines, is happening across the whole construction sector, not just within rail. The High Speed 2 (HS2) project in Britain aims to be net-zero carbon from 2035, with the target of all of its construction sites being diesel-free by 2029.
HS2’s first completely diesel-free site is the Canterbury Road vent shaft in South Kilburn in northwest London, where the Skanska Costain Strabag joint venture (SCS JV) has introduced a range of diesel-free technology and greener equipment.
This includes a 160-tonne Liebherr fully electric crawler crane, three of which are being used across the HS2 project, the use of biofuels such as hydrogenated vegetable oil to power plant and machinery on site, an electric compressor, and access to mains power on a 100% renewable energy tariff.
Other technologies used at the site include:
- an “EcoNet” which controls and reduces energy output from key appliances, reducing power demand by 30%
- non-road mobile machinery retrofit solutions which add pollution control equipment onto older vehicles as an alternative to replacing the machine or the engine, reducing emissions
- proactive dust management solutions
- fully electric renewable energy using solar and wind to power onsite equipment, and
- hydrogen trials considering both fuel-cell technology and combustible hydrogen solutions.
Alternative methods currently being explored include the use of modular construction systems. Bollinger says this can reduce waste, limit the number of vehicles moving to and from a site, and reduce the impact on the environment.
“We’re looking at plant rooms, for example, or mechanical and electrical rooms that are constructed off-site and then simply plugged in, with the intention that you’re not taking all these things to site and then bringing them all back again. It’s all done in the same place in a controlled environment and just dropped in,” he says.
While it is important to develop techniques and methods to ensure buildings can be constructed in a more sustainable way, infrastructure managers and other project managers need to be aware of these and specify them when going out to tender.
“The clients and the authorities need to accept or approve new solutions… because you cannot stick to the old things that you used to,” Bollinger says. “You have to approve new materials, solutions and approaches more quickly as well.”
An example of this is Dutch infrastructure manager ProRail, which in 2009 launched the CO² performance ladder (see panel) as an instrument that encouraged suppliers and contractors to reduce their emissions, thereby reducing operational costs and enhancing innovation. The higher a company ranks on the ladder, the more competitive that company is when bidding for ProRail tenders.
“This is not only about knowing that there’s a lower footprint cement available that you can use in your concrete, but this is also about your mindset and a change of culture and behaviour,” Bollinger says. “If people are more aware, they proactively come up with other ideas or suggestions or initiatives. I think that’s a very powerful change which started 20 years ago but step-by-step is just getting into the DNA of the sector.”
Rail must remember that it is not alone in seeking to reduce the impact of construction. There is a real opportunity to develop and benefit from economies of scale by working with other sectors. Successful adoption of this approach will ensure future projects are sustainable from conception to completion.
The CO² performance ladder developed by ProRail in 2009 is an instrument that helps organisations cut emissions, thereby reducing operational costs and enhancing innovation.
The criteria for the ladder are divided into four parts:
- insight: the organisation is aware of the different energy streams used within the company and this understanding determines the carbon footprint of the business
- reduction: ambitious reduction goals are developed and drawn into an energy action plan
- transparency: the organisation communicates to internal and external stakeholders on its CO² policies, and
- participation: the organisation participates in a sector initiative to share ideas with other organisations to reduce CO² emissions.
The higher a company is on the ladder, the more competitive its submission is when bidding for projects tendered by ProRail, with other public bodies outside the rail sector now also adopting this standard.