Joint modeling of schedule- and frequency-based services in public transport assignment models

Public transport networks today are getting increasingly complex with many lines and possibilities to go from origin to destination. When passengers make their route choice in a public transport network they cannot depart at the minute they want, but must wait until the first departure on the considered line. But how do passengers plan their route if they have a combination of high frequent and low frequent services under the assumption that passengers do not consult the timetable for high frequent services? This paper describes a framework to include both schedule- and frequency-based services in a joint model. Such networks are found in most major cities and especially in the greater Copenhagen area where there is a mix of frequency-based services such as A-busses and the metro and schedule-based services as the S-train and local bus lines. Four different transfer types are identified when transferring between schedule- and frequency-based services. These include a type where the passenger transfers from a frequency-based to a schedule-based line. In this case the passenger has a probability to reach the first departure on the schedule- based line, but can in some cases also miss the first departure and must wait for the next departure. A choice set generation method is developed using the event dominance principle to exclude alternatives which are above a certain threshold. This gives a choice set which is used in a discrete choice model (MNL). On this basis, it is possible to distribute the flow across the different alternatives. Two example cases are used to show the methodology: DTU to Copenhagen Airport and DTU to Brønshøj. The results indicate that there the framework can handle the two types off lines. It is found that the desired departure time, parameters in the utility function and the choice of threshold is crucial to find the correct choice set and distribution of flow across the alternatives. But there is also found improvement points in the choice set generation technique, but especially the discrete choice modelling should be investigated further to include that passengers can take decisions en route.

当前公共交通网络日趋复杂，线路数量繁多，乘客从起讫点出发的出行路径选择空间愈发多元。乘客无法按照自身期望的时刻出发，仅能等待所选线路的首班班次发车。但若假设乘客不会查询高频服务（high frequent services）的时刻表，那么在同时面临高频与低频服务（low frequent services）组合的场景下，乘客该如何规划出行路径？本文提出了一种可将基于时刻表的服务（schedule-based service）与基于频率的服务（frequency-based service）整合至同一联合模型中的框架。这类混合服务网络在绝大多数大型城市均有分布，尤以哥本哈根大区为典型：该区域同时涵盖基于频率的服务（如A线公交与地铁）与基于时刻表的服务（如S型列车与当地公交线路）。研究识别了基于时刻表与基于频率的服务之间的四类换乘类型，其中一类为乘客从基于频率的线路换乘至基于时刻表的线路。在此场景下，乘客有概率赶上基于时刻表线路的首班班次，但在部分情况下也可能错过首班车，进而需等待下一班列车。本文采用事件占优原则（event dominance principle）开发了一种选择集生成方法，可剔除超出特定阈值的备选方案，由此得到的选择集将应用于离散选择模型（多项Logit模型，MNL）。基于该方法，可实现不同备选方案间的流量分配。本文选取两个案例场景对所提方法进行验证：丹麦技术大学（DTU）至哥本哈根机场，以及丹麦技术大学（DTU）至布伦兹霍伊。研究结果表明，该框架可有效处理两类服务线路。研究发现，期望发车时刻、效用函数中的参数以及阈值的选择，对获取正确的选择集以及备选方案间的流量分布至关重要。此外，本研究也发现了选择集生成技术的改进空间，尤其是在离散选择建模领域，需进一步探究乘客在出行途中进行决策的相关问题。