Current article is about research of possibilities for improvement of sustainability definition for sustainable transport solutions, facilitating sustainable development of public transport system. Research will give a more complete look to definition of sustainability and will be the source of new scientific ideas, as well as ways of thinking about the public transport system and its sustainable development. There are a lot of definitions of sustainability, but they are scattered in different sources of information. There are not fully defined in literature principles of public transport system sustainable development. Modern researches show, that it is not easy to find perfect definition of sustainability, especially facilitating sustainable development of transport system. The definition must be analyzed and improved, as well as formalized if it is possible. Analysis of definitions and interpretations of sustainable development and sustainability and summarizing of principles of sustainability and sustainable transport system, will give a huge positive impact to development of transport area using sustainability principles. Current article is a part of the new cycle of researches about sustainability and improvement of its definition. Discussion based researches about sustainability will help to find better understanding of transport system sustainability and related topics. Enhancement of sustainability definition is a way to the improvement in quality of sustainable transport solutions.