Friends of the Earth are proposing that bus travel in the UK be free for under 30s. They hope it would help bring down greenhouse gas emissions when people abandon driving.
Provisional official data shows transport accounted for 34% of carbon emissions, with road transport the most significant source of pollution, in particular passenger cars.
The environmental campaigners suggests that to meet goals to curb global warming to no more than 1.5C above pre-industrial levels, large scale changes to transport are needed.
Reports says even with a faster switch to electric cars and cutting carbon emissions from the electricity grid, a reduction of at least 20% in the number of miles driven by car is needed by 2030.
So it proposes extending the current free bus pass scheme for older people to those who are aged 30 and under, and calls for local authorities to consider making bus travel free to everyone over time.
There are countries where free bus travel is already happening, including more than 30 in the US and 20 in France as well as in Poland, Sweden, Italy, Slovenia, Estonia and Australia.
Such a move deliver other benefits such as reducing traffic and noise, improving air quality and boosting health.
Before it could happen in the UK, the public transport system would have to be re-regulated and sources of funding would have to be put in place.
They are proposing free bus travel for the under 30s at first, before widening the scheme. They believe it would make for more liveable cities and cut damaging greenhouse gas emissions.
Three times more journeys are done by bus than train and they are the main means of transport for the car-less quarter of the population.