Bus bunching: a comprehensive review from demand, supply, and decision-making perspectives

Public transport service reliability is crucial for all stakeholders, including users, operators, and society. Bus bunching, where two or more buses on the same route travel closely together, significantly undermines service reliability. This paper reviews bus bunching, its causes and consequences, and control strategies from demand, supply, and decision-making perspectives. It identifies gaps in the literature, emphasising the need for realistic evaluations of control methods and real-world applications. The paper reveals that most bunching solutions prioritise operators over public transport users, and the trade-offs posed by these methods require further examinations. Hybrid methods combining holding with other measures have outperformed standalone holding methods but need real-world testing. User-centric approaches, such as encouraging and incentivising passengers to choose less crowded vehicles or wait, have demonstrated some potential in alleviating service bunching. However, their effectiveness in real-world applications present important research directions. In summary, the practical classification and framework presented in this review can assist policymakers in making informed and optimised decisions by considering various variables and performance measures involved in the process, and in finding balanced solutions for passenger and operator.