The Green Bus only appeared in the 1986 annual story, You Never Know. The bus was mentioned by Toby in a story about his old tramway that he told to Thomas and Percy. Toby and Henrietta were unhappy with the buses taking all their passengers, but got their passengers back when the bus crashed onto some roadwork.
This bus appears to be based on an AEC Regal "T Class" London Country Area bus. Bertie is also a member of this class.