Bus bunching
From Wikipedia, the free encyclopedia
Bus bunching is the phenomenon whereby a bus that is late tends to get later and later as it completes its run, while the bus following it tends to get earlier and earlier. The end result is that the two buses eventually form a pair, one right after another, and the service breaks down as the headway degrades from its nominal value. The buses that are stuck together are called a bus bunch or banana bus and may involve more than two buses.
The reason bus bunching occurs is because the time it takes for a bus to complete station duties is related to the number of people it is already carrying and the number of people attempting to board or disembark at a given stop. The bus that is already late tends to attract a higher number of riders due to the higher service gap between it and the previous bus; this in turn results in delays to the bus, delaying it further. Adding to this effect is the difference between individual drivers in terms of the speed of operation; some drivers are faster than others, resulting in inevitable catching up on long routes or high frequency routes.
Bus bunching is an example of chaos theory in action. The orderly procession of buses is inherently unstable and buses will tend towards bunches if left unchecked. However it is impossible to predict from the outset which buses will be bunched and which buses will proceed on schedule to the destination.
The phenomenon is well known in transit literature and has been well researched by transit planners and transit engineers worldwide.
According to "Progress Has Passed Metrobus By", a December 27, 2005 article by Lyndsey Layton of the Washington Post, one cause of bus bunching may be the intentional acts of bus drivers themselves. In the article, an anonymous Metrobus driver implies that some lazy bus drivers, who don't want to work and just want to get by, bunch intentionally so that the bus ahead of them picks up more passengers and thereby decreases their own workload.
