Travelling by foot or bicycle are clearly the most eco-friendly options, but in practise distance, 
weather and other practical considerations mean that the majority of journeys boil down to a choice between the private car/motorbike and public transport. Electric bikes powered by rechargeable batteries can now offer a viable alternative for urban commutes in some circumstances.
Where longer distance journeys are concern the choice is usual air, sea, rail or coach and for most of us the combination of time constraint and distance often means that air is the favoured choice. Aeroplane travel is usually sited as the greatest transport related threat to the environment, but confusingly its current share of CO2 emissions in the UK is around 6% compared to total road transport at 24%. The concern comes from the fact that Air travel is the fastest growing contributor to greenhouse gas emissions and it is particularly damaging because it creates these emissions at high altitude so there effect is much more corrosive on our atmosphere than the same amount of emission release at ground level. You can find more detail in our information page on Flying in this section.