Ecologically preferred types of drive systems for city buses—the context of the Polish energy mix

The energy mix determines the external costs of transport and the benefits from investments in the drive systems perceived as more environmentally friendly, such as electric vehicles. The aim of this article was to present a methodology to determine the environmentally preferable urban bus drive systems (electric, hydrogen, CNG, hybrid, plug-in hybrid, and diesel) depending on CO2 emission factors related to the production of electricity in a given country. The developed methodology was exemplified by the Polish energy system. The results indicate the environmentally preferable types of urban bus drive systems, taking into account vehicle exploitation. The results obtained can inform the decision-making process and, in particular, enable state administrations in EU countries to define a support mechanism for public transport (e.g., through subsidies) that is appropriate to the environmental benefits of operating particular types of vehicles under country-specific energy mix conditions.