Changing to a greener route

Arup’s design for the HS2 Interchange Station now underway near Birmingham sets new standards for sustainability as well as connectivity. Tom Boddy reports

Although it was recently confirmed that HS2’s overall scope has been severely truncated, with Rishi Sunak announcing that the northern leg beyond Birmingham was being cancelled, a major scheme to the south east of the city remains in progress. The design for one of what were four major transportation hubs for HS2, in Solihull, has impressive green credentials, with it being claimed as “the first train station globally to achieve BREEAM Outstanding certification.”

Currently at the design development stage with major works expected to start in 2024, the Arup-designed scheme will play a “crucial role” in the HS2 network, serving the West Midlands, Birmingham Airport, and the National Exhibition Centre (NEC), while also connecting to the UK motorway network.

Client HS2 Ltd selected Arup through a competitive process to lead the development of a “fully assured” design that not only “aligned with HS2’s requirements” but also achieved a “Schedule 17 planning permission in accordance with the HS2 Design Vision,” explains Kim Quazi, director at Arup.

The site for the station is situated within a ‘green triangle’ formed by the M42, A45, and A452, east of the NEC. This location was chosen particularly to ensure excellent connectivity to local transport networks, serving the wider West Midlands region and facilitating easy access to local and regional rail and road networks.

The project will function as a “regional gateway,” and also increase connectivity to key destinations like the NEC, Birmingham International Railway Station, and Birmingham Airport – all of which will be connected to the new station via an Automated People Mover.

The Interchange Station features two 415-metre-long island platforms and serves six tracks (two for high-speed through trains). This design accommodates up to five 400-metre-long high-speed trains per hour in each direction. The primary station concourse is situated west of the platforms, opening onto a public plaza to the north west and connected to the eastern side by a pedestrian bridge. The station’s design also includes facilities such as parking, taxi ranks, drop-off and pick-up points, and bus stops.

Arup completed the scheme design for the station in 2019, and the project is currently in the detailed design phase, which is being managed by the design and build contractor Laing O’Rourke.

Brief & concept development

Throughout the concept design phase, the team made a constant effort to ensure they took a “holistic, integrated multidisciplinary approach” to the design, bringing together a large team of core and specialist designers.

In the early stages, the team explored four primary options for where the station ‘box’ itself should be located. Two options looked at the potential of locating the station immediately adjacent to the trace (the track’s position in the landscape), while the other two placed the station ‘off trace’ to the east and west. These options were deliberated upon during a particular mentoring session of the HS2 Design Panel, and it was during this session that the idea of siting the station box to the west of the trace gained substantial traction.

The architects challenged the brief throughout the design stage to “ensure the proposal provided value-added benefits across the multi-disciplinary design and achieved an effective and simple solution.”

The design responsibility for the track itself and rail systems was outside the scope of Arup’s involvement. But for the station, the focus was on prioritising design that is “purposeful, simple, efficient and beautiful.” This was extended to cover how the team used digital tools. The analytical design tools used by the various disciplines were linked together, so design changes could ‘cascade’ through all work disciplines in real time. “A full BIM model was developed, and all disciplines worked through a single co-ordinated model within the site boundary.”

In terms of sustainability, HS2’s initial brief was centred around the goal of BREEAM Excellent certification. The team, consisting of ‘core’ and specialist designers, worked in close collaboration to enhance the project’s early stages. This involved optimising the building’s shape, form, and orientation, as well as adopting an energy strategy that was rooted in a fabric-first approach.

The result exceeded the original objective by the delivery of a scheme that is on course to achieve BREEAM ‘Outstanding’ certification, which is according to the architects, will be the first train station in the world to achieve this while maintaining a zero “regulated” carbon footprint.

This design response reinforced the sustainability credentials by using a ‘leaf’ concept that extended from the timber roof design to the station concourse below. This helped to signal a design that sought to “touch the ground lightly” in terms of its low environmental impact.

Arup emphasise that through a rigorous process of user engagement, they created a design steeped “in the unique landscape characteristics of the site,” which in particular maximised views across the Hollywell Brook Valley.” This approach further strengthened the rationale behind the ‘leaf’ concept.

Layout & operation

The station’s design incorporates several key elements that combine to optimise functionality and passenger experience.

The main station is positioned to the west of the platforms towards Hollywell Brook Valley, which connects to the platforms via two overbridges, one to the north and one to the south. A central pedestrian bridge spans the tracks, providing easy access to the taxi drop-off area. “Leveraging the site’s topography,” plantrooms and station back of house operational areas are situated beneath the main concourse.

Inside the main concourse, passengers have comfortable waiting areas, retail spaces, and a variety of food and beverage options.

The station accommodates six high-speed lines, with four directly linked to the station. Four generously sized platforms are configured as two platform islands, each 415 metres in length and 12 metres wide. In the centre of the railway layout, two high-speed lines allow trains to speed through the station at their maximum velocity. The station’s placement is carefully aligned with the platforms and the existing site context. “In broad terms, the layout is symmetrically arranged around the centre of the platforms,” says Quazi.

The purpose of this was to ensure equal distribution of vertical circulation to the platforms and a centralised control line to support intuitive navigation and simplify operation. Circulation from the control lines to the platforms is via the ‘paid concourse gallery.’ The concourse is designed “predominately off-trace,” says the architect, i.e. not aligned with the track, thereby “simplifying its structure and improving constructability.”

Automated People Mover

The Automated People Mover (APM) system will transport passengers and visitors between HS2’s Interchange Station, the NEC, Birmingham International rail station, and Birmingham Airport. The design aims to make it environmentally friendly as well as  “efficient, accessible, and reliable.” With the capacity to carry up to 2,100 passengers per hour in each direction, it will complete the journey in just six minutes.

The APM system has been designed with a “pinched loop configuration,” accommodating vehicles equipped with cable or self-propelled technology. The terminus stopping points, namely the Birmingham Airport Stop and Interchange Station Stop, are situated on a single-track viaduct, each featuring one platform.

The stops at the International Station and NEC each have two platforms, with the People Mover diverging around them. Within these stopping points, one platform caters to westbound travel, while the other facilitates eastbound journeys. An additional double track is included connecting to the maintenance facility, allowing two rail cars to pass each other “gracefully” along the viaduct.

To ensure the APM system seamlessly integrates with the main station, the station points and maintenance facility were developed by a similar core team of designers and both projects replicate the same architectural and engineering design methodologies and approaches.

Design vision: working with nature

The overall design vision for the station and surrounding site is “rooted in an ambition to work with the nature that surrounds it,” explains Quazi.

The station’s form has been carefully designed to reflect the rural landscape while strategically positioned to maximise views of the nearby valley. It focuses on merging with the existing natural landscape by working with the existing topography, and is situated on the site to minimise regrading of the ground levels.

The North West Plaza and the station’s front are positioned at the natural edge of the Hollywell Brook Valley, with the land descending a gradient toward the brook. “This allows the podium level accommodation to be fitted under the concourse while remaining outside the brook’s flood zone,” says Quazi.

The concourse level’s south-facing terrace provides a “panoramic view” of the valley’s gradual descent. At the platform level, the design eliminates the necessity for retaining walls to support the eastern drop-off area. Except for the station and bridge abutments, users are provided with either views of striking green embankments, or the picturesque surrounding countryside.

The roof takes the form of interlocking diamond-shaped ‘leaves,’ meticulously designed to “work with the environment,” says the architect. The glazed structures face towards the north, not only bringing diffused natural light into the station concourse, but also channelling any rainwater to storage for later use.

Near the station building, a rainwater harvesting tank will be installed to facilitate this. The system will include an underground water storage tank that pumps collected rainwater to an internal rainwater supply interface and control unit. The gathered rainwater will then be employed within the station premises and on the platforms for various non-potable purposes, such as flushing WCs and urinals.

A new gateway

The station’s architecture has been created to fulfil its pivotal role as the “gateway to the West Midlands.” Embodying that presence, as passengers step onto the concourse, they are greeted by a “vista of trees that frame Solihull,” with the NEC and the airport visible in the background.

Taking advantage of the setting in this way, coupled with the station’s naturally-inspired roof design, creates a “sense of arriving at a destination in its own right,” asserts Quazi.

The expansive canopy, extending over the Western plaza, not only provides shelter but also frames scenic views of the public spaces surrounding the station, enhancing the experience of arrival. The station also provides a unique vantage point which allows passengers to view the high-speed railway tracks below. This is located on a generously-proportioned pedestrian bridge specified with high-quality finishes to create a pleasurable passenger experience, allowing them the “opportunity to reflect on a journey in prospect or just completed.”

Sustainability wins

The expectation-surpassing BREEAM ‘Outstanding’ certification for the design was the result of a painstaking focus by the team, and the thoughtful selection of strategies and materials. This has culminated in the blueprint for one of the world’s most environmentally friendly railway stations yet built in the UK.

One key sustainable aspect of the station is how the roof is made from glulam timber, which delivers multiple benefits. It significantly reduces the project’s embodied carbon footprint, not only for the roof itself but also by allowing for lighter and shallower concrete foundations. Quazi says: “We have worked with the existing site topography to remove requirements for retaining walls in the wider site.”

The station will incorporate over 2,000 m2 of solar panels generating zero carbon electricity – they will be located on the canopies over the car parking spaces for people of reduced mobility, for ease of maintenance.

The energy created from this array will be used to power the building’s air source heat pumps, providing both heating and cooling for back-of-house facilities, communication systems, and plant rooms serving the rail systems. It will also contribute to the station’s general power provision and facilitate electric vehicle charging in the station’s car park. A proportion of the PV provision will also be used to serve the Automated People Mover (APM)’s maintenance facilities to achieve the zero regulated carbon aim. Cycle storage houses 176 bicycles with further room for expansion.

One of the main engineering and design challenges that Arup encountered was to ensure the concourse area was unheated and uncooled (with only natural ventilation provision), while achieving the HS2 internal temperature criteria for both winter and summer. Controlling the relative humidity of the concourse was also crucial to guarantee the durability of the timber roof and reduce the risk of condensation on the facade. The building physics, architecture and engineering teams have collaborated closely to achieve this, and simulations were carried out to predict the internal temperature and relative humidity of the space, against the structural timber requirements and condensation risk on the facade.

The building envelope provides the primary level of protection against adverse external conditions, both in summer and winter. During the early stages of the project, a key priority was to determine the required U-values and air permeability of the envelope to ensure thermal comfort and reduce the condensation risk.

During periods of high footfall in cold weather, where the main entrance doors are open for extended periods, air curtains will be used when required to further reduce the risks of cold draughts and discomfort.

Project into the future

This significant contract for both client, Laing O’Rourke and Arup is valued at around £370m, and will require more collaboration between O’Rourke and HS2 Ltd, across its two distinct stages. Initially, the teams will finalise the detailed design, followed by the construction of what is likely to become an iconic station in the area over the following several years.

As well as being highly sustainable, the station is set to boost the local Solihull economy. Arup’s inclusion of what is a grand public forecourt has been designed to allow for future development to help support this growth. Stakeholders such as Arden Cross, the Urban Growth Company (on behalf of Solihull Council), the West Midlands Combined Authority and others, are developing opportunities to help maximise the economic potential.

According to HS2, the ambition is to create of 30,000 jobs as a result of the new Interchange Station and its ancillary facilities, as well up to 3,000 new homes, and 70,000 m2 of commercial space.