Propulsion Technology Trends Across Major Bus Operators in Europe, North America and South-East Asia

Propulsion Technology Trends Across Major Bus Operators in Europe, North America and South-East Asia


Judith Michelle Cohen, RTSC, Imperial College London, Mark Trompet, RTSC, Imperial College London


This paper examines what bus propulsion types operators consider to be good environmental practice, the costs and practical barriers to implementation, and the decisions operators are taking as a result.


Bus organisations occupy a distinctive position with regards to energy and the environment. On the one hand, buses make an important contribution to pollution minimisation and carbon footprint reduction by providing an alternative to private car transport. Thus, the economic sustainability of bus organisations contributes to environmental sustainability. On the other hand, buses themselves require fuel and maintenance, which may use limited resources and emit pollutants either at the source or in the area where the buses operate.
In addition to balancing these concerns, these decisions cannot be made solely by the bus organisation on economic or environmental grounds – political/regulator involvement and public pressure both have the potential to impact the decisions made by (or on behalf of) bus organisations. Furthermore, there are cost implications to implementing environmental procurement policies beyond simply the cost of vehicles and fuel, which need to be understood.
This study examined the environmental decisions being made by members of the International Bus Benchmarking Group (IBBG). The IBBG, which is facilitated by the Railway and Transport Strategy Centre (RTSC) at Imperial College London, comprises 13 members in 14 cities, all of which provide normal passenger public bus service operations in large urban areas. The participating organizations are TMB, Barcelona, Spain; STIB, Brussels, Belgium; Dublin Bus, Ireland; IETT, Istanbul, Turkey; RapidBus, Kuala Lumpur, Malaysia; Carris, Lisbon, Portugal; London Buses, UK; STM, Montreal, Canada; NYCT and MTA Bus, New York, USA; RATP, Paris; SMRT, Singapore; KCM, Seattle, USA and CMBC, Vancouver, Canada. Honest and open sharing of data is enabled by a confidentiality agreement, which means research results are presented in an anonymised form.
This paper examines what operators consider to be good environmental practice, how much it costs to implement, and the decisions operators take as a result. In particular, the study used a benchmarking approach to understand the comparative costs and benefits of different fuel technologies as compared with a diesel baseline, considering purchase cost, fuel consumption, tailpipe emissions, and CO2 emissions, as well as supplementary costs such as the need for specific additional infrastructure or equipment.
The study identified that IBBG members are moving away from conventional diesels, towards alternative propulsion including hybrids, compressed natural gas and biodiesel. This trend is already well under way: only two of thirteen members are not planning to move towards hybrid buses in the next five years. The second trend identified is newer: ten out of thirteen members are planning to test or procure electric buses in the next five years.
Whilst electric battery buses are emerging as the next major technology that may be widely adopted, the study identified significant practical issues that need to be addressed before operators consider electric battery buses to be viable beyond test fleet status. Batteries do not currently provide the range that operators need to run a full schedule as they would with diesel buses. Solutions therefore need to be found in terms of enhanced battery capacity or charging during service hours. Operators in Europe and North America are beginning to test on-road charging solutions including induction plates and pantographs. However, the battery electric bus technologies currently available continue to have significant practical and operational disadvantages in terms of infrastructure costs, increased layover or dwell times, and lack of interoperability of different manufacturers’ solutions. We conclude that plug-in hybrids, trolleybuses with off-wire capacity, and new battery technologies all point to a future in which the barriers to fleet-wide electrification will be overcome, but that this will use technologies still currently in the early stages of development.


Association for European Transport