Hybrid trolleybus for Berlin-Spandau

The hybrid trolleybus combines the proven technology of conventional trolleybuses and state-of-the-art battery charging technology. A solution that helps protect the environment, enabling the city to offer future-oriented services. However, it also requires appropriate infrastructure.

How can the operation of hybrid trolleybuses be implemented so that it makes sense both economically and ecologically? PTV's feasibility studies provide answers to this question.


Project description

In order to examine the possibilities, feasibility, efficiency, and possible contribution to emissions reduction of a trolleybus system, the BMVI commissioned the project “Feasibility of hybrid trolleybus operation – Berlin Spandau” as part of the German Federal Mobility and Fuel Strategy (MFS). During the study, PTV’s experts compared the bus system with other operating and charging concepts for electric buses and different implementation variants in the current network.

The project was conducted in cooperation with the IFB Institut für Bahntechnik GmbH and the Technical University of Dresden (Prof. Stephan). PTV was in charge of the project management.

Initial situation and advantages of hybrid trolleybuses

Hybrid trolleybuses are locally emissions-free. Therefore, they can contribute to reducing local carbon dioxide emissions and global greenhouse gas emissions. Electrically powered vehicles using electricity from an overhead line – in some cases buffered in a battery – are particularly efficient. Hybrid trolley buses fulfill the criterion of being emissions-free, but they require an infrastructure with various design options.

The hybrid trolleybus unites the proven, reliable technology of conventional trolleybuses and state-of-the-art battery storage technology. It thus enables high-performance, reliable operation without restrictions, especially for lines with high numbers of passengers and long line blocks. Thanks to energy storage (traction batteries) on board, the vehicles, junctions, intersections, and route sections where electrification would be difficult or is not desired for aesthetic reasons, can even be navigated without the overhead line. This creates free space for a compatible, technically flexible design of the electrical network infrastructure.

Electrification concept for Berlin

As part of the wide-ranging electrification plans for the entire bus fleet of the Berliner Verkehrsbetriebe BVG by 2030, the installation of overhead lines is being considered for some parts of the line network that should be used by several lines.

In Berlin Spandau, state-of-the-art battery-hybrid trolleybuses could run approximately 50-65% of the time with overhead lines and thus also charge their batteries. The buses could then run the rest of the route in battery mode without the overhead line. What some people refer to as in-motion charging is what Berliners call “route chargers” for their hybrid trolleybuses.



The length of the network examined is approx. 235 km. 14 bus lines were analyzed for the deployment of up to 187 hybrid trolleybuses (articulated and double-articulated buses). Various scenarios were formulated for the configuration of the electric vehicles with energy storage and design and dimensioning of the electrical DC 750 V network infrastructure. A key finding of the study: A hybrid trolleybus system for Berlin-Spandau is technically feasible and economical.


Various development scenarios

Based on scenario A, which served as initial scenario with a high share of overhead lines, a scenario B was developed iteratively with a minimal share of overhead lines. In scenario C, according to the Berlin local transport plan 2019-2023 and the state’s public transport demand plan, the intended implementation of a tram in Berlin-Spandau was considered in the form of reduced operation for the hybrid trolleybus. Here it was assumed that individual bus lines will be replaced by the tram.



The technical study revealed that the share of the overhead line required for the variants recommended for realization is between 63% (scenario B) and 54% (scenario C) of the respective network lengths.

An economic feasibility study was conducted based on the results of the technical feasibility study. For this, the investments and ongoing operating costs for a period of 30 years were determined for the scenarios of the hybrid trolleybus system. These were compared to the operating costs for conventional diesel bus operation and other possible electric bus technology variants (depot charging and occasional charging at the end points, end-point charging).

When looking at the overall cost, that is, the project-specific life cycle cost calculation, the annual costs per kilometer driven of the various hybrid trolleybus scenarios are comparable to and lower than the electric buses that are depot or occasional chargers. This is mainly due to the fact that fewer vehicles are required when using hybrid trolleybuses, which also results in lower operating expenses - since thanks to recharging while driving, no additional charging at the end points or in the depot is required.

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