From today if you take a second bus journey, within an hour of the first, it won’t cost you any more than you paid for the single journey. IF, you use contactless for payment or use an Oyster card.
This also applies if you use a TfL Tram journey and connect to or from a bus.
We are promised that in 2018 this will be an option to make unlimited bus and tram journeys within the hour. Remember you have to board the second bus within an hour of boarding the first bus, not of getting off it.
But for now, enjoy the savings that this is going to bring.