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Environmental pollution is likewise characterized by noise emissions. As a result, according to the European ambient noise directive 2002/49/EG, noise pollution of inner-city areas, in particular congested urban areas, is a major issue of the future European policy. In areas of bus stops and roofed installations, such as bus stations, there are high values of disturbing noise emissions induced by urban bus traffic. Concerning this matter, hybrid urban buses are able to offer promising solutions for an effective noise emissions reduction. At the Institut für Kraftfahrzeuge (ika), RWTH Aachen University, the project "HYBOB," financed by the BMWi (Bundesministerium für Wirtschaft und Technologie), is being conducted in cooperation with the EvoBus GmbH/Daimler Buses. The project is aiming to design and develop a highly sophisticated serial-hybrid diesel-electric propulsion system for urban bus applications.

The reduction of fuel consumption remains an important criterion in the development of new vehicles. Apart from parameters such as drag and rolling resistance, the efficiency of the drive train also plays an decisive role. Following a concentration on the engine and transmission over the past few years, attention has now turned to apparently less important components such as axle joints and how these can be incorporated into the fuel consumption reduction process. Since the transmission losses of axle joints are relatively low, “classic” methods to determine the efficiency (such as MD-measurements using wire strain gauges) are inapplicable due to the attained accuracy. A new method has thus been developed at the Institute of Automotive Engineering (ika), which enables a very accurate recording of the efficiency of joints (±0.03 percentage points).

In April 1996 the European Project „Electric Vehicle Fleet Demonstration with advanced Batteries” has been started with financial support of the European Commission. Sixteen electric vehicles equipped with ZEBRA batteries have been built up as prototypes and are now operating in five major European cities. Today, after 1½ years of fleet operation the fleet of 10 OPEL Astra Impuls has covered a mileage of more than 275.000 km and the project can be evaluated sufficiently exact to extrapolate the project results. Energy consumption structures, mobility structures (daily trip length) and user acceptance have been analyzed and will be discussed in detail.