Integration of hybrid buses-towards a clean fleet in public transport

Basic Information

Mobility solution ID







Thematic areas

Clean & energy-efficient vehicles
  • Cleaner fleets


ASEAG, the mobility service provider in Aachen is increasingly converting the bus fleet into environmentally friendly buses in order to curb noise and emissions. Within CIVITAS DYN@MO, three hybrid buses have been tested and one of them has been converted into a fully electric bus and represents the first electric articulated bus used on a bus line in Germany.

Implementing sustainable mobility

ASEAG is the largest mobility service provider in the Aachen region. It aims to convert its buses step-by-step into an environmentally friendly bus fleet. The company aspires to identify the optimal bus and create an innovative high mobility bus system to connect the new Campus Melaten area, but also to identify possibilities to connect European neighbors (Belgium and the Netherlands) with the new innovative bus fleet.

ASEAG currently has a fleet of 211 buses. Of these, 68 are solo buses and 128 articulated buses. Because of an increased passenger demand, overall eight double-articulated buses have been purchased between 2005 and 2007 and at least seven CapaCity buses between 2010 and 2013.

Since 2005, all obtained buses have been equipped with particulate filters. Currently 167 buses (79%) have a particulate filter, which is well above the average of North Rhine-Westphalia. In the near future, the whole fleet is expected to feature this technology. It is worthy to note that ASEAG started to test hybrid buses in 2008.

Five hybrid buses were tested within CIVITAS DYN@MO. A fully electric articulated bus (the first one in Germany) and 5 lightweight buses have been put into daily operation. Another important factor for the successful deployment of electric buses on the streets of Aachen was the charging infrastructure.

The main objectives of this measure were:

  • Reduction of noise emissions in public transport by implementing hybrid buses
  • Reduction of CO2 and particle emissions in public transport by about 20%
  • Reduction of energy consumption of buses in public transport by 20%
  • Increased understanding of an innovative, low emission bus technology for the decision-making process concerning the future fleet
  • Initiation of the renewal of the public transport fleet (launch of tendering process)



The works were very advanced and were completed by the end of 2016.

Planning & preparation
During the preparation phase the following tasks were executed:

  • Revision and adaptation of current testing programme, considering better the special topographic situation in Aachen
  • Definition of test phase for two further hybrid buses, one MAN and one Mercedes-Benz bus (1 solo bus and 1 articulated bus), e.g. routes, time table, etc.
  • Establishment of a database of present experiences from cities with hybrid buses covering various operational and topographical conditions
  • Comparative analysis of tests : catalogue of indicators and weighting of indicators and results – establishment of a decision matrix; evaluation indicators considered the CIVITAS core indicators where possible
  • Approval of leasing contracts for further hybrid buses. The rental of a EURO VI hybrid prototype bus was planned for the second half of 2013. The technical development was watched very closely. It was important to test vehicles in different variants (for example buses with capacitors or batteries as energy storage system or serial/parallel hybrid drive systems)
  • Equipment of two hybrid buses and one conventional vehicle with acoustic measurement devices in order to perform specific noise and vibration measurements in the interior. In this way relevant acoustic and vibration data referring to passenger comfort was collected. The measurement campaigns  pursued the time schedule of project partner ASEAG.
  • Equipment of two hybrid buses with sensors and loggers for the collection of operation data (fuel consumption, driver behavior, traffic situations, etc.).
  • Rental of a Mercedes Citaro G Hybrid (articulated bus). This bus fit perfectly into the current ASEAG fleet because there was a high proportion of Mercedes-Benz vehicles. Workshop staff was very well trained in repairing this bus type and most spare parts were available in stock. Because of its technical specification the bus was very suitable for a conversion. ASEAG has been planning the upgrade into a fully electric environment so that it is possible to drive 50 km without any diesel engine.

Implementation & demonstration

In the implementation phase the following tasks were executed:

  • Test operation with two hybrid buses in real conditions according to the defined test programme
  • Collection (logging) of all important acoustic characteristics, regarding real bus stop arrivals and departures in scheduled operation. And limited traffic measurements in designated areas (e.g. in traffic calm zones). In addition, reference measurements  were made at the measurement noise route of the “Institut für Kraftfahrzeuge” (Institute of Automotive Engineering).
  • Data acquisition of relevant acoustic characteristics regarding real bus stop arrivals and departures in scheduled operation. In addition, acoustic measurements were performed on the pass-by noise test track of the “Institute of Automotive Engineering”. The major aim wasto verify the potential of hybrid urban buses in terms of an effective reduction of noise emissions. The measurement cam­paigns pursued the time schedule of project partner ASEAG.
  • Collection (logging) of data concerning the fuel consumption and the driver behaviour (driving style) was conducted
  • Conversion of a serial hybrid drive bus into a fully electric vehicle using a Fast Charging Station at the ASEAG home depot. This bus operated under real conditions from 2014 onwards.
  • Procurement of four hybrid buses based on the evaluation results; the precondition for the procurement was the reduction of fuel consumption by at least 20%
  • Procurement of five light weight buses based if benefit/cost-ratio was higher than 1.0 and introduction into ASEAG’s bus fleet



Tangible outputs:

  • Three hybrid buses were tested and results analysed
  • Purchase and placement into daily operation of a MAN, hybrid solo bus
  • Purchase and placement into daily operation of a Mercedes articulated hybrid bus
  • Comparison the suitability of hybrid and electric vehicles
  • Tender for further renewal of PT fleet
  • Integration of low emission vehicles (hybrid- ,fully electric- and lightweight) into ASEAG’s marketing strategy, with the objective to inform its citizens/customers
  • Awareness campaigns for the public
  • Information brochure/flyer for citizens/customers
  • Information meetings with stakeholders
  • Training was organised for 10 employees as multipliers for further bus driver training
  • Training for 80 drivers was provided by the multipliers


Expected outcomes in the short- to medium-term:

  • Definition/identification of the optimal low emission bus system for Aachen and the region
  • Incremental improvement and renewal of PT fleet

Expected outcomes in the mid- to long-term:

  • New PT fleet consisting of low emission vehicles
  • Improvement of air quality
  • Reduction of noise emissions and improvement of quality of life for residents

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