In public transport, bus bunching, clumping, convoying, piggybacking or platooning refers to a group of two or more transit vehicles (such as buses or trains), running along the same route, which were scheduled to be evenly spaced, but instead run in the same place at the same time. This occurs when at least one of the vehicles is unable to keep to its schedule and therefore ends up in the same location as one or more other vehicles which are supposed to be behind it.