The tramway or BRT – which is greener?

Overall, tramways have a smaller carbon (CO2) footprint than bus rapid transit (BRT) systems. This is the key finding of a study by Alstom and Carbone 4, released this November 4.

Tramway Citadis Rabat MAroc
Rabat-Salé tramway, Morocco: in Rabat, up to 120,000  people travel every day aboard its trams. The city is now planning to extend the one-line network. Studies have shown that two lines should lead to a CO2 emissions reduction of about 30,000 tonnes per year

Taking on board infrastructure construction, the manufacture of rolling stock, and subsequent operations, the survey compares five alternatives – the classic tramway, optimised tramway (Attractis), electric BRT, hybrid rechargeable BRT, and classic diesel BRT.

The analysis, completed on a typical 10km line operated in Belgium, demonstrates that for equivalent transport capacity, over a 30-year lifetime, a tramway system emits about half as much CO2 as a BRT system operated with diesel buses, and around 30% less than a BRT with hybrids.

Explained Julien Blanc, associate director, Carbone 4: “For transport, studying greenhouse gas [GHG] emissions are complicated because they linked to many factors. We need to work on all these aspects – mobility needs x modes x energy efficiency x C02 content of the energy used [coal, petrol, biogas], and the type of electricity, e.g. how it’s produced –  when seeking to reduce GHGs.”

“The energy and transport sectors are closely linked, yet infrastructure is often ignored when talking about the carbon impact of the latter.” pointed out Cécile Texier, sustainable development director, Alstom.

Highlights of the study, and related points, include the following:

  • a diesel BRT generates half the CO2 emissions of a classic tramway during  construction of the route and manufacturing of its buses
  • however, following these initial phases, the carbon emissions advantages of a tramway outpace all BRT systems, with its  operations (traction energy) emitting four times less C02 than a diesel BRT
  • Attractis is designed to generate 20% less emissions during the construction phase than a standard tramway. It can be fully operational within 30 months
  • standards governing the leaking of refrigerant gases, which contribute to C02 emissions during operations, are more stringent for the tramway (rail) than BRT
  •  apart from the bicycle, the tram is one of the greenest urban transport modes in service today, thanks to its low environmental impact when in operation

“The survey conducted with Carbone 4 illustrates that rail systems have a lower carbon footprint than other motorised modes,” said Ms Texier. “It also shows that an optimised system like Attractis, […] can significantly reduce CO2 emissions from the construction phase.”

Demographic projections show that the global population is expected to reach 9.7 billion people by 2050, with 70% living in urban areas. With annual global urban transport emissions expected to double to nearly 1 billion tonnes of equivalent CO2 by 2025, public authorities are more concerned than ever about the environmental impact of transport.

Reducing greenhouse gas emissions from transportation is both a key issue and an exciting challenge,” said Mr Blanc. “It should be achieved through relevant urban planning, energy efficiency, clean energy and, of course, modal shift. Tramways are  part of the solution and these infrastructures will benefit from all the improvements aimed at ‘cleaning’ the electricity mix.”

From 2017 in France, 40% of the energy for Alstom’s facilities will come from renewable sources guaranteed by supplier EDF. “Yes, it’s a bit more expensive than standard electricity,” admits Ms Texier, “so we are closely weighing up the economic balance of this approach and will progress realistically on this front.”


Measuring up

At COP21 (December 2015), Alstom announced its energy objectives. They essentially comprise two commitments – to reduce the energy consumption of its transport products by 20% and slash by 10%  the energy and carbon intensity of its operations (both compared to a 2014 baseline) by 2020.

Since none previously existed, the company has itself defined standard methodologies for energy simulations. Designed to ensure the consistency of collected data, they are based on sets of assumptions defined for each type of rail vehicle, e.g. mission profile, occupancy, temperatures, and so forth. And Alstom apparently has no qualms about sharing these tools with a wider audience…

“Of course we couldn’t possibly  apply the same hypotheses for, say, a tram and a high-speed train,” explained Ms Texier. “Now these methodologies are completed, we are ready to share them with the rest of  the transport industry.”

The company has already performed simulations of the energy consumption of its tram, metro, regional, and mainline vehicles – both for 2014 and current reference versions. “Working together with our clients in countries including France, Spain, Brazil, and Germany, we now have a more precise understanding of energy consumption and savings, and how they work, than before,” said Ms Texier.

Examples of Alstom’s work with customers and suppliers to boost the energy efficiency of trains and railway systems include:

  • an innovation partnership with French Railways (SNCF) to design a new generation TGV (high-speed train) that has 20% more capacity, consumes 20% less energy, and is 90% recyclable
  • a project with the Railway Procurement Agency (RPA) in Dublin involving two trams fitted out with intelligent counter equipment; the results are “very postive”
  • Railsponsible, an initative created in March 2015 to promote sustainable procurement across the industry supply chain. Alstom is one of the seven members, which include SNCF, Bombardier, and Dutch rail operator NS


Photo credits: Alstom







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