a stream of vehicles except for motorcycles, which train does not allow for safe rejoining the train after passing or overtaking.
an uninterrupted stream of several vehicles where each vehicle can be overtaken individually and distance between individual vehicles allows for safe rejoining the train after passing or overtaking.
an uninterrupted stream of several vehicles where each vehicle cannot be passed individually and distance between individual vehicles does not allow for safe rejoining the train after passing or overtaking.