The contrast between the historical and the futuristic could scarcely be greater than the example currently being provided in Dresden. Passengers on the bus route 62 are experiencing this in person as they glide past the most wonderful monuments and squares of Dresden in an electrically-operated Mercedes-Benz Citaro articulated omnibus. The first three of, in total, eight Mercedes-Benz Citaro G BlueTec®-Hybrid vehicles ordered were presented to Reiner Zieschank, member of the Management Board of Dresdner Verkehrsbetriebe AG (public transport operator) on 19 May 2011 on the Theaterplatz square by Konstantinos Tsiknas, Head of Sales for the Mercedes-Benz Bus and Coach unit in Germany.

The hybrid buses will be deployed primarily on the high volume and high-frequency 60s bus routes in the future. The benefits of the sustainable hybrid technology will be exploited to best effect on these routes. Changing topography, the proximity to the city centre and the buses’ high capacity provide ideal conditions in which to prove the vehicles’ suitability for prolonged daily use. The number of hybrid vehicles even makes it possible to run a complete line with them. Whole sections of the network could thus be operated electrically.

The Citaro G BlueTEC® Hybrid is currently the only hybrid bus available that can cover 9-kilometre-long sections of the route solely on electric power - i.e. without using its diesel engine - and that drives nearly noiselessly up to bus stops. It continues on its route after each stop in exactly the same way, without the usual loud engine sound associated with buses. The drive system comprises four electric wheel hub motors that source electricity from one of the largest lithium-ion batteries ever used in mobile applications. Electricity is generated through braking when the bus is driving downhill, for example. If required, it can also be produced using a generator driven by a diesel engine that is relatively small for the Citaro’s vehicle category. Experts call this type of system a series hybrid drive.

This technologically advanced diesel-electric hybrid concept has been implemented in the tried-and-tested articulated variant of the world’s most successful city bus series – the Mercedes-Benz Citaro. Externally, the hybrid Citaro looks just like a conventional diesel bus. The only difference is a higher roof to house the battery. The real difference becomes apparent once the bus starts moving. Operating smoothly and virtually silently, the four electric motors accelerate the 18 metre bus very quickly. Boasting a combined output of 320 kW which, if required, can also be provided by the battery and the diesel-driven generator, these motors are installed close to the wheel hubs of the centre and rear axles. The motors are also used when the bus brakes, acting like generators or bicycle dynamos as they transform braking energy into the electricity used to charge the battery. Should the battery require more energy, the diesel engine is switched on automatically to produce additional electricity. This diesel engine is only half the size of the combustion engine generally used in diesel buses, and weighs only 450 kg (as opposed to 1000 kg). It also boasts a 4.8-litre engine capacity instead of the usual 12 litres. And its 160 kW output is approximately one-third lower than that of a conventional diesel bus engine.

As its energy storage device, the new Mercedes-Benz Citaro G BlueTEC® Hybrid uses a lithium-ion battery with an output unprecedented in this performance category. The battery system generates a maximum of 240 kW and, weighing less than 350 kg, is comparatively light. Key advantages over conventional battery systems include a higher energy density, high storage capacity, and low weight. By way of comparison, hybrid drive buses tested in Stuttgart 30 years ago used 3000 kg lead batteries. Lithium-ion batteries first came on the market in 1991. Today they can be found in virtually all devices that combine high energy requirements with low weight, e.g. mobile phones, digital cameras, camcorders, and notebooks. It was only relatively recently, however, that they began to be used in large vehicles like passenger cars, trucks, and buses. The use of lithium-ion batteries in buses is nothing new for Daimler. More than 900 of the 2850 hybrid buses on the road which are produced by Orion (a Daimler AG brand in USA), the global market leader for hybrid buses, are already equipped with lithium-ion batteries manufactured by the company that supplied the battery system for the new Mercedes-Benz Citaro G BlueTEC® Hybrid. The output of this system corresponds to that of approximately 9000 large laptop batteries.

Over 400,000 passengers use the public transport network operated by Dresdner Verkehrsbetriebe every day. In addition to buses and trams, cable cars and ferries also form part of the public transport offering in the capital of Saxony, which is used by inhabitants and tourists in equal measures. The public transport operator runs 29 bus routes with a bus fleet of 145 vehicles.
Vehicle procurement, such as the recent hybrid fleet additions, is based on the principle of sustainability, as is Dresdner Verkehrsbetriebe’s corporate philosophy as a whole. By creating an attractive form of local public transport, the transport operator would like to contribute directly to the development of the city in an ecological, economic and socially acceptable way. With 1703 employees and 94 apprentices the public transport operator is the most important employer in Dresden.