Factors that affect the evolution of headway variability along an urban bus service

Headway variability in public transport: a review of metrics, determinants, effects for quality of service and control strategies

“…(i) Headway variability at the beginning of the route: it is one of the chief variables that influence headway regularity of buses along a route, as shown by several empirical studies using automatic vehicle location data (Arriagada et al, 2019;Diab, Bertini, & El-Geneidy, 2016;El-Geneidy et al, 2011;Hammerle et al, 2005;Soza-Parra et al, 2021). Godachevich and Tirachini (2020) identify three groups of variables that are significant in influencing headway variability at vehicle dispatching: first, operation and design of the network, as variables such as length of the route, the average passenger demand, the travel speed and the scheduled frequency affect the reliability of travel times and therefore the arrival of vehicles at terminals; second, operation and infrastructure of terminals and depots, including variables such as the complexity of rolling stock circulation associated with a given terminal and the distance between a depot and the first stop of the service; and third, the performance of the incumbent public transport service provider, as different operators take different actions to control headways at dispatching.…”

“…(iii) Distance travelled from the beginning of the route: As the vehicles progress along a route, they face different sources of uncertainty on demand, traffic flow, incidents, etc., making it difficult for buses to keep regular headways, i.e. without proper control, the probability of bunching increases as buses move forward along routes (Chen, Yu, Zhang, & Guo, 2009;Figliozzi et al, 2012;Sáez et al, 2012;Soza-Parra et al, 2021). (iv) Passenger demand and dwell time variability: As suggested by the model presented in the Appendix, the larger the passenger demand and the boarding and alighting times per passenger, the larger the increase of headway discrepancies along bus routes.…”

“…Larger boarding and alighting times per passenger also increase the variability of dwell times (Sun, Tirachini, Axhausen, Erath, & Lee, 2014), which further leads to increases in headway variability. Therefore, upgrading from slow to quick fare collection systems and passenger boarding rules (such as the implementation of off-board payment stops) has the potential to significantly reduce headway variability (Soza-Parra et al, 2021;TRB, 2020a). Finally, it has also been found that infrequent stop activity such as the operation of lifts increases headway variability as well (Albright & Figliozzi, 2012;El-Geneidy et al, 2011).…”

“…Because of its relevance for users and operators alike, headway variability in public transport is a problem that has been widely studied during the past decades. Several factors have been found to worsen bunching particularly in the case of bus services, such as service frequency, passenger demand, traffic congestion, number of bus stops, number of traffic signals and route length (Arriagada, Gschwender, Munizaga, & Trépanier, 2019;Figliozzi, Feng, Lafferriere, & Feng, 2012;Moreira-Matias, Ferreira, Gama, Mendes-Moreira, & de Sousa, 2012;Soza-Parra, Muñoz, & Raveau, 2021). Irregularity of bus dispatching at the beginning of a route is a key variable that increases bus bunching along a route (Arriagada et al, 2019;Hammerle et al, 2005;Soza-Parra et al, 2021).…”

“…Several factors have been found to worsen bunching particularly in the case of bus services, such as service frequency, passenger demand, traffic congestion, number of bus stops, number of traffic signals and route length (Arriagada, Gschwender, Munizaga, & Trépanier, 2019;Figliozzi, Feng, Lafferriere, & Feng, 2012;Moreira-Matias, Ferreira, Gama, Mendes-Moreira, & de Sousa, 2012;Soza-Parra, Muñoz, & Raveau, 2021). Irregularity of bus dispatching at the beginning of a route is a key variable that increases bus bunching along a route (Arriagada et al, 2019;Hammerle et al, 2005;Soza-Parra et al, 2021). Fleet control strategies are usually proposed to deal with the problem of headway unreliability, such as bus holding, station skipping, deadheading, speed control, boarding limits and traffic signal priority (e.g.…”