# Planning-Level Optimisation of Headway Regularity
## 2 Literature Review
Stop skipping is another commonly researched method [54; 59; 60; 61; 62; 63]. An example of a limited-stop bus service with vehicle overtaking is given in [PERSON] et al. [63], while some authors combined vehicle holding and stop-skipping methods [57; 64]. In addition to vehicle holding and stop skipping other methods have been developed to manage headway variability in real time, whereby the most studied methods are based on allowing buses to overtake each other [65; 66] or regulating speed [67; 68; 69]. Considering that operations at stops have a large impact on vehicle bunching, a significant number of authors have opted to focus on reducing the vehicle dwell time by restricting boarding [47; 51], increasing the boarding intensity by allowing entry through all available gates [70], or validating tickets before boarding [71]. In a recent study, the authors did not directly restrict passenger boarding, but relied on passengers' desire for comfort and encouraged waiting for a less crowded vehicle. As a part of their work, [PERSON] et al. [72] examined the effect of providing passengers with real-time congestion information on vehicle bunching reduction. Similarly, [PERSON] et al. [65] demonstrated that, when passengers are sufficiently informed and can choose which vehicle to use, this not only improves the journey experience but also reduces vehicle bunching. In a recent study dealing with the control strategy based on real-time information, [PERSON] et al. [73] identified a significant gap between the recommendations based on recent theories and modern practice. According to these authors, closing this gap requires the adoption of appropriate technology and software for continuous communication between the control centre and the driver. On the other hand, [PERSON] [29] examined the main contributors to headway reliability and reached the following conclusions: (I) bus lines with long routes, high occupancy,and mixed traffic have very low reliability; (II) a headway disturbance that occurs at the beginning of the line tends to propagate along the line; (III) accuracy is important for lines with long headways, whereas precedence should be given to uniformity for lines with short headways; (IV) service reliability and transport speed on bus lines can be improved by reducing the number of stops on the line, the dwell time, and the impact of mixed traffic on vehicle movement between stops. According to the available literature, the influence of line length and number of stops on headway uniformity and service reliability remains insufficiently studied [29; 45; 74]. Using a case study in the Hague, [PERSON] [74] investigated the effect of line length on service reliability. The author split the routes of longer lines and analysed the resulting service reliability and passenger travel time based on real data. The obtained results indicate that splitting the line increases service reliability while reducing passenger waiting time at the bus stop as well as time spent in the vehicle. The author further noted that the time loss due to headway variability can be reduced by about 30% when the line is split at a stop with low passenger flow. However, technological advances are being increasingly harnessed to deal with headway disturbances in real time. In particular, methods based on Automatic Vehicle Location (AVL) systems are being proposed despite their limited practical utility due to the lack of appropriate technology and software. Therefore, several authors advocate for greater reliance on planning-level strategies as a means of increasing the PPT resistance to headway disturbances. While in most cases this approach has yielded positive results, the proposed methods are typically developed from the operator's perspective, offering limited insight into the effectiveness of these strategies from the passengers' point of view. The work presented in this article attempts to fill these gaps.