Just shy of a decade into its delivery, Crossrail has released its environmental legacy – a stack of nearly 500 in-depth documents, reports and analyses into the process of building Europe’s largest infrastructure project. The resource reads as a step-by-step guide to the efforts to minimise disruption and pollution stemming from the delivery of the £14.8bn project.

Preparing to open in December 2018, the Elizabeth Line amassed more than 100 million hours of work into connecting Reading to Shenfield, bypassing Heathrow Airport and Abbey Wood along the way. It is expected that 200 million passengers will use it each year, bringing an extra 1.5 million people within 45 minutes of central London.

Apart from the impact on jobs, the economy, business and connectivity in the congested capital, Crossrail was always going to be a huge disruptor to the everyday lives of communities and the natural ecosystems lying in its path. For just over three years, eight giant tunnel boring machines burrowed underneath the heart of London to construct 42km of new rail tunnels.

But all of the early concerns voiced during the project’s initial stages, regarding levels of noise, destruction of natural habitat, as well as threats to architectural and archaeological heritage, were mitigated by a transparent and conscientious construction process. Unlike its sister project HS2, which from the beginning has been affected by fierce opposition from campaigners and organisations such as The Wildlife Trusts, Crossrail avoided sparking anger on this scale and as a result, no notable public campaigns set out to take it down – a truly remarkable feat for a project of this size.

Ever since the publishing of the Crossrail Act in 2008, which gave the delivery organisation the power to construct, maintain and operate the Elizabeth Line, “best practice became the project’s minimum environmental requirement”, according to the project’s assessment reports. Early into the environmental assessment process, a number of key areas of concern were highlighted, such as the fate of excavated material, dangers posed to archaeological treasures, the carbon dioxide footprint of construction, as well as use of natural resources such as concrete and steel.

Crossrail’s latest environmental management paper, published in September, confirmed that the main challenge had been to minimise these impacts as much as possible without compromising the need to deliver the project on time and within budget.

“Crossrail not only set a new precedent for delivery of a truly ambitious 21st Century infrastructure project, the strategic approach they took in managing the many environment and sustainability challenges was exceptional,” says Martin Baxter, chief policy advisor for the Institute of Environmental Management and Assessment (IEMA).

Minimising construction impacts

Tunnelling works for Crossrail began in May 2012, and over the following three years, teams worked around the clock to dislodge more than three million tonnes of excavated material.

Recognising the impact this extensive project would have on wildlife, Crossrail partnered with the Royal Society for the Protection of Birds (RSPB) to use the material in creating a wetland nature reserve at Wallasea Island in Essex, home to tens of thousands of migratory birds, in addition to it being a natural barrier to threats from climate change and coastal flooding. This was just part of the total 98% of material excavated from sites which was reported as “beneficially reused”.

Although the construction phase amounted to the release of 1.7 million tonnes of CO2, the carbon emission statement shows that the project exceeded its initial target of 8% CO2 reduction, reaching up to 11% reductions in 2014-2015. This equated to a saving of about 52,000t of CO2 emissions.

In building the underground infrastructure, Crossrail also trialled the use of CemFree, a cement-free material that helps significantly reduce the CO2 emission impacts of concrete. Citing technical difficulties, as well as lack of current standards in using this new product, CemFree was not used in the end, but the trials are hoped to build “confidence in the use of this material in future infrastructure projects”, according to the project’s website.

Further carbon and cost reductions were achieved by using LED lighting and by powering generators with electricity rather than fuel. Although the apparent physical constraints of Crossrail’s sites prevented the use of renewable energy, Whitechapel station has been flagged as the only site capable of supporting solar panels for the station’s future energy requirements.

In addition, all of the underground infrastructure, including tunnels, portals and shafts, have achieved Excellent ratings under the Civil Engineering Environmental Quality (CEEQUAL) methodology so far.

Powering sustainable transit in the years to come

But Crossrail’s green efforts aren’t restricted to the construction phase.

For example, Crossrail’s underground stations became the first to be assessed under the Building Research Establishment Environmental Assessment Methodology (BREEAM), in the hope to provide an assessment tool that can be used for future underground station projects. A full BREAM assessment of the entire project is expected to be released in March 2018.

In delivering its new rolling stock, Crossrail partnered with Bombardier in an attempt by the former to try to “reverse the trend of other recent UK rolling stock builds” by using trains 50t lighter than usual. The Class 345 trains were fitted with regenerative braking, as well as driver advisory systems which guide the driver to use optimal energy-efficient driving techniques. These trains will also be washed with harvested rain water, reducing the need to use mains water.

As with any public transportation project, the pollution created during construction is expected to see a payback once the line starts operating, shifting traffic off London’s streets. For Crossrail, the payback period is envisioned to be between seven and 26 years after opening, with annual savings of between 70,000t to 225,000t of CO2. In total, it is forecasted that 2.5 million tonnes of carbon savings will be achieved by Crossrail, from the start of the construction programme through to operation over the next 120 years.

“The team achieved what seemed impossible through a governance structure that insisted on sustainability,” Baxter says. “The key thing they got right was embedding environment as a central, critical theme from the very beginning, considering environment and sustainability as a vital area alongside engineering and project management.

“Their approach to collaboration, engagement and influencing has also been impressive – essential skills for an environment and sustainability professional. By harnessing those skills, Crossrail extended the reach of a 15-strong environment team to 10,000 other professionals across the project and set a new standard for collaboration on infrastructure projects.”

A full assessment of the project’s approach and targets is expected after its completion in 2018.