This is calculated by taking the tonnage that is committed to rail over an agreed number of years, and calculating out how many lorry journeys will be removed.
Cyfrifir hyn drwy nodi'r tunelli yr ymrwymir i'w cludo ar y rheilffyrdd dros nifer cytûn o flynyddoedd, a chyfrifo faint o deithiau lori na fydd eu hangen o ganlyniad i hynny.