A greener solution
Public transport has long been toted as one of the answers to greenhouse gas emissions – the more people riding a bus, the fewer cars on the road. However, bus manufacturers have not stopped there, instead choosing to focus on developing the most sustainable transport solutions attainable through modern technology.
According to United States (US)-based commercial vehicle manufacturer, Navistar, adding just one standard diesel school bus to the road is equivalent to removing 36 cars, as far as saving energy is concerned.
Why? Because transportation, while not the biggest contributor to global warming and greenhouse gas emissions, is still a major contributor to climate change. In South Africa, transport accounts for 31.1% of each annum’s CO2 emissions. According to the Union of Concerned Scientists (UCS), based in the United States, US vehicles alone emit more CO2 than most other countries emit from all their energy sources combined.
“Cars and small trucks make up two-thirds of the transportation emissions problem, so getting people out of their cars – and into buses for example – and providing efficient vehicles powered by renewable fuels are high priorities,” says UCS’ website.
“This shift to mass transit not only decreases emissions of carbon dioxide, but also reduces air pollution, lowers oil imports and curtails congestion,” it continues. “Simply taking transit more often lowers the impact of our travel, but improving the technology of bus service can greatly enhance the benefits of transit.”
South Africa is currently in the early stages of implementing bus rapid transit (BRT) in all its major city centres, and while BRT will most certainly reduce the country’s overall carbon footprint, this public transport system at least is more a social response to local conditions than an environmental one.
That is not the case in more developed countries, however, where fuel and engine advancements are aimed at meeting the challenges posed by climate change.
UCS’ website examines the various options available in this evolution of cleaner buses, which is certainly one of the most progressive segments in the commercial transport sector in terms of “greener” vehicles.
Says the website: “The first stop in the evolution of cleaner buses has been to use cleaner-burning fuels. These new combustion buses use the same engine technology as diesel buses, modified to burn ethanol, methanol, propane, biodiesel or natural gas.”
Scania introduced its first ethanol hybrid bus in May 2007, a full-size low-floor city bus capable of cutting fossil CO2 emissions by up to 90% if fuelled with ethanol, and saving at least 25% fuel.
“Scania sees no reason to wait for other new fuels and technologies that could become viable in 10 years’ time,” said Hasse Johansson, group vice president of research at the Scania Technical Centre in Södertälje, Sweden, at the world premiere of the manufacturer’s ethanol hybrid bus in Helsinki.
Twelve conventional ethanol buses equipped with Scania’s hybrid-drive system started regular operations in Stockholm during 2008 and 2009, in cooperation with the city’s public transport operator, SL (Storstockholms lokaltrafik).
Scania considers ethanol to be by far the most cost-efficient renewable fuel on the market today, taking into account factors like availability, infrastructure and access to proven technology. Converting a conventional diesel engine to run on ethanol also involves a reasonably simple process.
UCS’ website also discusses hybrid and electric buses: “Hybrid buses combine a combustion engine with electric motors and batteries,” explains the website. “Hybrid buses promise lower emissions and higher fuel economy than traditional combustion buses. Electric buses, powered by batteries, are also in the early market stage and produce zero emissions.”
Volvo Buses launched its new Volvo 7700 Hybrid bus model in October 2008, receiving its first order from a bus operator in Luxembourg – who ordered six hybrid buses – shortly thereafter. Delivery started this year.
The order was signed in the presence of Luxembourg’s transportation and environment minister at a large transportation symposium arranged by Sales-Lentz, one of Luxembourg’s largest transport operators.
The topic discussed during the symposium was how public transport could contribute to fulfilling the Kyoto Protocol. “One way to contribute is to operate with buses that have lower fuel consumption and thereby lower emissions,” said Jos Sales, one of the partners of Sales-Lentz.
“But to be able to choose such buses on a large scale, it must be economically viable. This is the reason why we selected Volvo’s hybrid buses. Despite the higher purchase price, over time they yield a lower cost per kilometer owing to the substantial fuel savings.”
The bus model incorporates hybrid components developed by Volvo and offers fuel savings of up to 30%.
Volvo has chosen to develop a parallel hybrid in which a small diesel engine and an electric motor operate individually or together. The bus stores braking energy in batteries and uses this energy to power the electric motor. The diesel engine is shut down at bus stops and the bus drives away from the stop emission free and nearly noiseless, powered by the electric motor. When the bus reaches 15-20 km/h, the diesel engine starts up again.
According to the UCS, the most promising stop in the evolution of bus technology is fuel-cell buses powered by hydrogen. Using electric engines that combine hydrogen and air to produce electricity, fuel-cell buses release no pollution – the only by-product is water. However, heat-trapping gases may be emitted indirectly as a result of the process that produces hydrogen for the fuel cells. When the hydrogen is harvested from natural gas, the indirect emissions associated with fuel-cell buses are roughly half those of diesel buses. When the hydrogen is harvested from water, using energy from renewable sources like solar power, the indirect emissions are eliminated completely. Commercial application of fuel-cell technology in buses will pave the way for a technology that holds tremendous promise for the automotive and even electric power markets.
In September, Daimler received the F-Cell Award for innovative use of fuel-cell technology in the Mercedes-Benz Citaro FuelCELL Hybrid urban bus.
The Mercedes-Benz Citaro FuelCELL Hybrid made its public debut in June 2008 at the UITP Congress in Vienna. The fuel-cell hybrid bus is the first member of Daimler Buses’ new generation of fuel-cell buses. It combines the advantages of the diesel-electric Citaro G BlueTec Hybrid, which had been unveiled a few months earlier, with those of the hydrogen-powered Citaro fuel-cell buses.
The bus emits absolutely no pollutants while in motion, and is virtually silent, making it ideal for use in highly congested inner cities and metropolitan areas.
“Reducing air pollution from buses offers real economic benefits to urban areas struggling to address air-quality problems,” concludes UCS, estimating that in Los Angeles, for example, the emissions saved over the life of a natural gas bus are worth $56 000 (R448 000) in avoided costs for controlling industrial air pollution – costs that businesses and consumers would otherwise pay to meet clean air requirements. A hydrogen fuel-cell bus could save $151 000 (R1.2 million) in these costs over its lifetime.
“So far, clean air requirements have been a driving force behind the move to alternative-fuel buses. As global warming becomes a high international priority, however, technologies like fuel-cell buses that do double duty – both zeroing out air pollution and slashing heat-trapping gas emissions – will become even more important. But putting such buses on the road requires government leadership. Federal research programmes to continue developing these technologies and transit funding programs that help purchase advanced buses are critical,” insists UCS.