Transport group Go-Ahead, which owns the Oxford Bus Company, said 65 per cent of its buses were now designed to minimise air pollution.
Its latest environmental and social report is the first from the company to address staff, community and social issues as well as the environmental impact of the group's work.
Last year, the company's environmental report won the Institute of Logistics and Transport's Environmental Excellence Award.
This year, the company reported continued reductions in bus emissions, and stable carbon dioxide emissions, as well as increased waste recycling levels.
Go Ahead has also developed a life-long learning programme for staff, and free education packs for schools.
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