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| The last electric tram in Durban, South Africa, a then the largest trams in the world. |
Former town planner and Wheels writer Brian Bassett said all cities had tramlines in
those years, but these systems fell out favour because everyone thought crude
oil would always be sold for around R15 a barrel.
City engineers then cited studies to show how expensive the trams’
electricity was compared to cheap gasoline. Citizens supported their arguments,
as everyone aspired to be independent with their own car.
As a result, no one shed a tear when the rails were ripped up and
coaches sold for scrap across SA in the mid 1940s.
Now a comparison of the environmental lifecycle impacts of tramway
and Bus Rapid Transport (BRT) systems points out shows a return to trams,
instead of buses, are the way to go.
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| Modern trams are sleek and about as exciting as beige. |
Environmental consultants Carbone 4 was sponsored by tram builders
Alstom to conduct the study. Until recently, a lack of hard industry data made
it difficult to compare the long-term environmental performance of BRTs and
tramway systems, but Carbone 4 said all that changed last year, when Alstom
shared its data on standard tramway systems and its optimised Attractis
integrated tramway system.
Carbone 4 is a leading independent consulting firm based in Paris
specialised in climate-resilient and low-carbon strategy. Alstom develops and
markets complete rail systems, equipment and services in 60 countries with
31 000 employees. The result of their study was the world’s first comparison of
end-to-end carbon footprint of tramways with those of a range of buses deployed
in rapid transport systems.
Carbone 4 began by comparing Alstom’s data to BRT data issued by
leading French, European and international institutions.
The study took into account multiple variables, such as the fact
that a fully-electric bus with large batteries would have less room to carry
passengers.
It also factored in how often the vehicles would need to be
replaced — 30 years for a tram and 15 years for a bus — and wear factors, such
as battery lifetime for electric buses.
The study then analysed the CO2 emitted by the energy used to
build, maintain and renew the transport system and power the vehicles.
Regarding electricity, the study took into account the average
electricity carbon factor in Belgium, which has a mix of nuclear, hydro and
fossil fuel sources.
The sensitivity of the results to the emission factor of
electricity was also assessed.
Perhaps not surprisingly, considering the
sponsor, tramway systems emerged a clear winner when it came to supporting
cities in their goals to have cleaner air and cheaper mass transport, although the Carobon 4 team admit constructing the rails and overhead lines can make the place
messy for two years or more.
Construction and manufacturing
Although a bus system offers short-term
advantages during construction and manufacturing, when making a tram produces
400 tons of CO2 compare to making a diesel bus, which emits only 30 tons of CO2,
the tramway system is a clear long-term winner, with much lower overall lifetime
emissions, thanks to its better operation and maintenance performance and the
longer lifetime of the trams.
Due mainly to the combustion of diesel to power
the bus, a diesel BRT’s total lifetime emissions are more than twice as high as
the ones of a tramway system.
For the same reason, a plug-in hybrid BRT system emits about 30%
more greenhouse gas (GHG) than a tramway system over its lifetime.
The BRT system also uses more electricity than the tramway one with
a similar transport capacity. Even a fully electric BRT system has 17% higher
lifetime emissions than a tramway system, since a city would need to operate a
large fleet of buses to achieve the same transport capacity as 20 trams,
resulting in 3,6 times more kilometres traveled by a bus annually.
Because BRT infrastructure is lighter during the initial
construction phase, its associated emissions would be 2,2 times lower than for a
tramway.
If a city can use existing road infrastructure as a basis to build
a BRT system, it would however need to reinforce it for heavy traffic and build
stops and other associated elements.
Impact of energy mix
Electricity production accounts for more than
40% of global fossil CO2 emissions. Since tramways are powered solely by
electricity, how does the electricity mix influence the carbon footprint
advantage of tramway systems?
Even in a worst-case scenario in which the electricity emission
factor is around 0,800 kg CO2 per kWh, as in China, all other assumptions
remaining the same, the tramway’s carbon footprint remains lower on a 30-year
lifetime than a diesel, hybrid or electric BRT system.
Carbone 4 also predict the electricity emission factors will
significantly decrease in the coming years, thanks to the current developments
in the fields of renewable energy, which will reduce further the footprint of
electrical modes.
This ranges from new uses of silica which increases several 1 000
times the heat of heavy salts in solar energy capturing systems, to Tesla and
Solar City merging to form one company, to Toyota making a fuel cell car that
doubles as a mobile power generator.
After doing the study, Alstom had to get in a punt for its product,
the Attractis a tram service.
Altogether, over a 30-year lifetime, Attractis said in a statement
its tramway system will emit 57% less GHG than a diesel bus system, 32% less
than a plug-in hybrid, and 23% less than fully-electric bus system such as BYD
or Volvo uses. Alstom said a 12 km long Attractis tram system can be fully
operational within 30 months.
