The TMB bus fleet helps to improve air quality

The protection of the environment is one of the backbones of the strategic policies of TMB. As a public transport company, its activity is essential for the promotion of more sustainable mobility, and a clear alternative to private vehicle transport, which is less efficient and has a greater impact on the environment. However, TMB goes beyond this, and a strategic objective has been marked to reduce the environmental impact that its activity causes, such as consumption of energy and other natural resources on the one hand and as a generator of waste material on the other.

This concern is expressed in a constant search for cleaner and more efficient options for the propulsion of the bus fleet – an essential service that provides daily transport for 700,000 passengers on 108 bus lines that run through Barcelona and its metropolitan area.

In this sense, TMB has decided to use renewable energies in its installations and new fuels in its vehicles. The company is making a day-to-day effort in the research and experimentation of alternative fuels with the aim of contributing to the reduction of gas emissions causing global warming. In this way, currently nearly a quarter of the fleet (296 units of 1,086) consists of buses running on compressed natural gas which emit lower amounts of CO2, NOX and particles, and next year the proportion of those that use this less contaminating fuel will continue to increase. The aim is that these buses will eventually reach 40% of the total number of buses in service. With regards the diesel fleet, there are 120 units that use 30% biodiesel – a mixture of gasoil and vegetable oils that reduces emissions of carbon dioxide and other contaminants – and recently it has incorporated latest generation diesel buses with the Euro 4 and Euro 5 qualification, which comply with the most demanding environmental requirements.

As an example, the Euro 5 legislation implies that the buses have to emit half the levels of nitrogen oxides ( NOX) than the current levels of the current Euro 3 legislation. As far as the particles are concerned, the Euro 5 standard implies reducing all the emissions to a fifth of their levels. This adoption of cleaner gas and diesel engines implies a direct contribution to the improvement of air quality in the immediate environment and for the protection of the health of the population in the metropolitan area.

Among these measures, the obtenation of the ISO 14001 certification for the environmental management system of the bus on the public road, in 2000 is also worthy of mention.

Furthermore, during 2003 and 2006, TMB participated in the CUTE test project with electric buses powered by hydrogen batteries, giving 100% clean propulsion which could mature in the future, and are working in the new project HyFleet CUTE in order to experiment with hydrogen fueled buses, when the industry is able to provide them.

In addition, TMB has recently been the first transport company in testing with hybrid propulsion – the simultaneous combination of electric and thermic engines in a same vehicle. The chassis firm Castrosua has ceded us one prototype. It is a medium-sized unit (9.4 meters in length and with a capacity for a maximum of 50 people) which runs on two electric engines situated on the rear wheels. It also has a diesel engine which recharges the batteries when part of the charge has been used. Two months ago, this first prototype of the hybrid bus started on a trial run on different bus lines in order to quantify the results of energy and fuel saving which will be achieved. On these lines they have been making measurements of consumptions to be able to contrast them with those of the hybrid prototype. The next step is to compare the results of consumption and emissions with those of equivalent vehicles of conventional propulsion. If it is verified that the hybrid bus produces an important energy saving and has a good operation, then TMB will buy more units to reduce the environmental impact, if there exist a consolidated commercial offer.

With this technology – which has already been tested on automobiles and is beginning to be applied to heavy vehicles – a reduction of up to 30% is being achieved in the consumption of fuel and pollution emissions, such as monoxide and carbon dioxide, hydrocarburants, solid particles and sulphur oxides, which will have a direct benefit on air quality. In the case of nitrogen oxides, the expected reduction is of 50%, due to the optimum functioning of the engine.

Other advantages of the hybrid vehicles are the reduction in the noise levels, both externally and internally, as the electrical engines are much quieter than an internal combustion engine. According to the tests carried out, the reduction in the noise level may reach 50%.

It has to be pointed out that for passengers; electric traction also means an improvement in comfort, thanks to the smooth running of the vehicle. Acceleration is progressive, the driver applies the brakes more softly and there is no pulling as there are is no change of gears.

Another characteristic of the hybrid prototype is that it stores the energy that it produces in the braking process. When the driver takes his foot off the accelerator, the vehicle stops consuming energy from the batteries and takes it from the braking. Furthermore, when it is stationary, its consumption is zero.

In parallel, TMB is working on a project to provide hybrid propulsion to part of the diesel buses of its current fleet, by means of incorporating an electric synchronised engine. In order to move ahead with this technological challenge, TMB will work together with several companies established in Catalonia.

The project, which is at an initial stage, aims to update (technologically and environmentally) approximately one hundred units of the TMB fleet, as well as boosting the Catalan industrial sector in an interesting line of research, development and innovation. It is estimated that the diesel buses converted to hybrids generate direct benefits in the health of the population, thanks to the reduction of emissions and noise. In economic terms, it is expected that the saving in fuel will permit an amortisation of the investment.

Within the same line of promotion and support to clean technologies applied to public transport, TMB has become part of the consortium that promotes the project Ecotrans, financed by the Centre of Industrial Development of the Spanish Ministry of Science and Innovation. This is a four year research project with the aim of improving the mobility systems by means of technologies that make it attractive to the population and more efficient from the energy point of view. The participation of TMB in the Ecotrans project will consist of the planning and monitoring of the design of a new generation of technologically advanced buses in collaboration with the Agency of Urban Ecology, Applus-Idiada and the Centre for Innovation in Transport of the Universitat Politècnica de Catalonia.

In this context, in the future TMB will continue with the research and development of new bus projects related to the improvement of environmental quality and will cooperate on training programmes for company researchers and technicians and on educational issues.