That's among the unsurprising findings of a report by CENEX (the UK's centre of excellence for low carbon technologies), published today (25 February 2015).
The 'Green Fleet Technology Study for Public Transport' report was commissioned by the Public Procurement of Innovation in Action Network (PPIA).
Other key conclusions include ensuring that accurate costing mechanisms are incorporated into vehicle and R&M procurement, and also that operators and policy makers should set rigorous, holistic environmental goals at a city-wide level.
The aim of the study was to inform the PPIA network of the main technological advances and likely future developments in transport aimed at addressing climate change.
Drawing on information from industry technology roadmaps, interviews with technology providers and industry experts, the report establishes current procurement practises from the PPIA network cities and future demand for public transport vehicles.
The report focuses on alternative drivetrain technologies and fuels that offer carbon reduction from city buses, although technologies relevant to taxis are also discussed.
It describes the likely performance of short-medium term solutions (less than 10 years) and suggests side measures and practises that could be implemented to assist in the transition to cleaner public transport fleets.
"The report helps public authorities and operators to answer the question of 'how' and 'when' the many different low carbon technologies on offer can be supported," states states Chris Walsh, head of technical support and consultancy at Cenex.
"This report really helps us, as a city, to further strengthen the policy mechanisms needed to support and encourage the introduction of lower carbon and cleaner public transport," adds Hasan Wazir, climate innovation procurement manager at Birmingham City Council.
To download the full report, click on the link below.