Trolleybuses: Characteristics and Applications
(extract from Public Service Bus Systems with electric Propulsion,
Verband Deutscher Verkehrsunternehmen, 2007)
Project Editor, Prof. Dr.-Ing Adolf Muller-Hellman, VDV
Motivation and Political Framework for the Development of electric Propulsion Systems
� Environmental and Structural Advantages of Electric Traction Drives for Road Vehicles
� Power Demand for Regular Service Bus Operation
Electric Propulsion Motors
� Model Types of Electric Propulsion Motors
� Advantages of the electric drive train in comparison to automatic transmission
Catenary-bound electric Propulsion Systems
� Features of Modern Trolley Buses
� Catenary systems for trolley buses - designs and systems
� Buses bound by conductor rails
Flexible electric Propulsion Systems
� Service experiences with diesel-electric regular service buses
� From NEBUS to CUTE: Development stage of fuel-cell-powered buses Service experiences with fuel-cell-powered buses
� Maintaining hydrogen-fueled buses
� Preconditions for transit to �Hydrogen economy�
Energy storage systems and hybrid concepts
� Electrochemical energy accumulators (batteries)
� Electromechanical energy accumulator (flywheel accumulator)
� Electrostatic energy storage devices (ultra capacitors)
� Parallel and serial hybrid concepts vs. mixed hybrid
� Service experiences with a diesel-electric bus using an Ultracap intermediate storage unit
� Hybrid continuously variable transmission with battery storage
� Service experiences with a diesel bus using battery storage devices and concept of a fuel-cell-powered bus using battery and Supercap accumulators
� Electrically driven regular service buses -What does the future have in store?
Features of Modern Trolleybuses
The trolleybus combines basic advantages of the street car with those of the diesel bus and represents one of the most economical electric local public transport systems. New trolleybus systems are not only being developed all over the world but also already existing ones are being thoroughly refurbished and expanded as well.
Of course, individual systems are also being discontinued, but usually in order to be developed into a metropolitan railroad system due to an increased number of passengers.
A trolleybus can swing out approx. 4 m below the trolley wire on either side. Today, additional flexibility is usually required on modern systems. One would like to avoid road works under one's own "steam", possibly keep historic downtown areas or bridges free from overhead lines, and particularly allow for perfect freedom of movement on the machinery and equipment yard.
Overhead integration in a seperate trolleybus lane in Milan - transport capacity on dedicated roadways can be very high.
So dependence on the overhead system can be reduced through freely dimensionable alternative drives. Using modern energy stores such as batteries, flywheel accumulator systems or supercaps, routes of approx. 3 km in length can be driven without trolley wires. Longer routes free from overhead lines can be covered using diesel aggregates which can be designed, up to a full secondary drive (duobus) e.g. for overland rides.
Moreover, the trolleybus offers an answer to current political and ecological issues such as local air pollution, ever increasing contamination by fine dust in city centres and noise pollution for city dwellers. Since the trolleybus causes little to no emissions it reduces the strain on the health of the residents, thus enhancing their well-being. The combination of electric drive and rubber wheels reduces the noise emissions vs. street car and diesel bus, for instance. So the passage of a trolleybus is hardly noticed by passers-by and hence not felt to be a nuisance. Employing trolleybuses on main roads but also in auto free areas or traffic-calmed areas and residential areas will result in considerable enhancement of quality of life. Since the traction motor is switched off on a trolleybus at standstill, there is no background noise at bus stops, as opposed to vehicles with internal combustion engines. Residents in the vicinity of bus stops especially and particularly at terminals are enthusiastic about the hardly audible noises in comparison with a diesel bus or natural-gas bus.
The Basel transport authority has saved approx. 20-25% of the energy used by the trolleybus fleet fitted with flywheel accumulators compared to conventional trolleybuses on the same line. After over 10 years of use, the accumulators now average one repair/38,000 hours of operation.
The acceptance of this local zero-emission means of transportation is also demonstrated by a higher occupancy factor. Thus statistics from various public transport authorities show that the occupancy factor on regular trolleybus lines is up to 10-20% higher than on comparable diesel bus lines. This is certainly caused by the pleasant riding comfort of the vehicles, but also through the visible routing indicated by the overhead line. These features enhance passenger trust in the punctuality of the system. Moreover, various public transport authorities (such as in Salzburg) report an even lower accident frequency with trolleybuses as compared to conventional buses.
A Neoplan N6221 symbolically decorated for the Olympic Games in Athens. A European wide survey found a 10-20% increase in occupancy on trolleybuses compared with diesel bus lines.
So far, only electric drive systems have had the advantage of storing braking energy and to reusing it for the subsequent acceleration process. This can take place via onboard energy stores or, as common on trolleybus systems, energy is provided to other vehicles via the overhead line. As a result, the braking vehicle can provide vehicles driving uphill with a large part of the energy required particularly during extended uphill and downhill driving, and reduce the primary-energy demand of the fleet by up to 30%. And we must not forget that the electricity prices as a rule are not following the explosive increase in the price of crude oil due to the energy mix during electric power generation.
The energy consumption of the trolleybuses reduced by recuperation and the real cost advantages of electric current vs. diesel fuel as well as ecological benefits have led to the trolleybus regaining strength as a traffic system in many parts of the world.
The advantages of the trolleybus are being rediscovered in many places. The sound mixture of well-tested technology, innovation and environmental compatibility is demonstrated by successful traffic systems that are equally appreciated both by passengers and operators.
Publisher by Verband Deutscher Verkehrsunternehmen, 2007.
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Also reviewed -
Published by John Wiley & Sons, Inc. 2007.
Engineering pages -
Promoting quiet, clean urban transport using Overhead Electric, Zero Emission Trolleybuses -
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