The paper presents systematized environmental perils resulting from the operation of combustion engines. A serious environmental threat was identified in the sector of public transportation. Hence, pro ecological projects in the public transportation sector have been presented. As a particular ecological solution bioethanol E95 has been presented as an alternative fuel for diesel engines. An analysis of the emissions from city buses has been performed: conventional and hybrid buses, fitted with diesel engines, fuelled with diesel oil and bioethanol E95. It has been observed that the application of bioethanol E95 ready engines leads to much better pro ecological results than the application of hybrid solutions.