Trams greener than buses
Novel study shows cities battling smog and diesel engines will do well to go back to tramways
FEW residents of Pietermartizburg will have been around when the public transport needs of Scottsville were served by a tramway, which served the suburb with large wagons and had its terminus near today’s tourism office in the centre of town from 1904 to the 1936.
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.
Environmental consultants Carbone 4 was sponsored by tram builders Alstom to conduct the study. Until recent- ly, 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 fullyelectric 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 Carobon 4 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 travelled 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 plugin 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.
LEFT: This picture of Old Faithful, Durban’s last electric tram, was taken on August 2, 1948 in Musgrave Road outside Jameson Park. RIGHT: A modern- day electric tram in Brussels, Belgium.