John J. Bartholdi III of the Supply Chain and Logistics Institute at the Georgia Institute of Technology and Donald D. Eisenstein of the Booth School of Business at The University of Chicago, explain that maintaining headways between buses is very challenging.
From the report abstract: "Most bus systems try to achieve this by adherence to a schedule; but this is undermined by the tendency of headways to collapse, so that buses travel in bunches.
To counter this, we propose a new method of coördinating buses. Our method abandons the idea of a schedule and even any a priori target headway. Under our scheme headways are dynamically self-equalizing and the natural headway of the system tends to emerge spontaneously."
Bartholdi and Eisenstein say that they have tested their system successfully in Atlanta.