The cycle that produces clustering
Imagine two buses scheduled ten minutes apart. The first encounters a traffic jam or takes longer at one point. During that extra time, more passengers gather at the following stops. It then boards more people and falls further behind.
The second vehicle arrives at the same stops shortly after. As most of the passengers have already boarded the first one, it stops for less time and approaches. Without intervention, the distance between the two decreases until they begin to operate almost as a pair.
Possible causes
Research using automatic location data and passenger counts relates the phenomenon to variation in travel time, irregular demand, short intervals, spacing between stops and short recovery time at terminals. The same line may present different mechanisms in different sections.
- Congestion and temporary blockages.
- Slow boarding, crowding and accessibility at the stop.
- Irregular exits at the terminal.
- Broken vehicle or interrupted trip.
- Lack of interval control along the route.
What BuzuRadar can measure
With successive positions, it is possible to identify vehicles from the same line that are very close together for a period of time and observe whether the grouping is repeated. For a more rigorous metric, the ideal is to calculate the interval between passages at control points and distinguish between direction, variant and trip.
The map should not automatically assign blame. Two nearby positions can represent overtaking, a terminal, a detour, or different directions. The evidence becomes stronger when the pattern persists while the headway before or after the pair widens.