Public transportation sustainability is a multidimensional phenomenon that currently presents a relatively limitedly studied area of the greater sustainable transportation paradigm. Overall, sustainable mobility and urban transportation patterns have been discussed extensively in previous literature, yet research focusing solely on public transportation services remains minimal. Public transportation is a central component of both the larger urban sustainability ideology, and the efforts to minimize the negative impacts transportation has on our societies and the surrounding environment. Thus, the recognized knowledge gap regarding public transportation services and their sustainability ought to be addressed.
The basis of researching and understanding public transportation sustainability relies on the tri-dimensional approach of sustainable development established by the United Nations. The balanced view of the ecological, social and economic dimensions provides the initial framework for the research, and furthermore structures the more specific factors contributing to public transportation sustainability. As the majority of previous research discusses sustainable transportation as a whole, public transportation must be applied as a filter for the literature review in order to obtain a holistic view of what public transportation sustainability truly consists of, and what its special characteristics are. The end result of the literature review is a comprehensive and detailed definition of the nature of public transportation sustainability and a collection of specific factors that contribute to overall sustainability, i.e. sustainability indicators.
These findings are then organized under the ecological, social and economic dimensions, forming a sustainability assessment tool, referred to as the Public Transportation Sustainability Indicator List (PTSIL). The indicators include, for example, reduced greenhouse gas emissions, increased physical accessibility to public transportation services, and increased fare revenue. Each indicator contributes to the overall sustainability of the system, functions independently, and has been given a desired direction which will positively affect the system sustainability.
It is essential to keep in mind, that even though the indicators act independently, they must still be addressed in a balanced and comprehensive manner, as established in the PTSIL. Focusing on one indicator is disadvantageous and can potentially harm the overall sustainability. Thus, understanding the phenomenon as a whole, and addressing sustainability holistically, plays a key role in sustainability research, assessments, and practical planning processes.
In this research, the PTSIL tool was applied to two case cities, Helsinki and Toronto, through qualitative content analysis. The comparative research offers insight on how diversely sustainability can be addressed by different actors, and how the city specific results compare and relate to previous research. The PTSIL forms a lens through which the official content of public transportation agencies in Helsinki and Toronto could be carefully analysed and scored based on an ordinal scale that reflects the desired direction attached to the individual indicators, and how ambitiously those indicators and the larger themes they present were addressed in the content.
Both cities scored the highest in the economic dimension, while the social dimension presented the weakest results. However, the differences were massive in terms of individual indicators, which can be explained by the lack of an established definition of public transportation sustainability leading to diverse interpretations of the phenomenon, as expressed in previous literature. Additionally, the city specific results can be linked to the current urban conditions regarding land use and governance structures, indicating strong support towards transportation oriented development and regional coordination, as well as long-term commitment to plans.
Need for further research exists regarding a more detailed and dynamic understanding of the PTSIL indicators and their internal relationships, as well as their links to existing urban conditions. A comprehensive definition alongside an assessment tool regarding public transportation sustainability is thus needed in scientific research as well as practical transportation planning, and the established PTSIL offers an initial platform for such applications.