Quality on single-track railway lines with passenger traffic : Anlytical model for evaluation of crossing stations and partial double-tracks

Abstract: Railway transportation is showing a substantial increase. Investments in new infrastructure, new fast and comfortable vehicles, and high frequency of service are important factors behind the increase.Infrastructure configuration and timetable construction play important roles in the competitiveness of railway transportation. This is especially true on single-track lines where the travel times and other timetable related parameters are severely restricted by crossings (train meetings). The crossings also make the lines’ operation more sensitive to disturbances.Since the major part of the Swedish railway network is single-track it is of great interest to examine the relationships between operation properties, such as travel times and reliability, and infrastructure configuration on single-track lines. The crossings are the core feature of single-track operation and this thesis focuses on the crossing time, i.e. the time loss that occurs in crossing situations.A simplified analytical model, SAMFOST, has been developed to calculate the crossing time as a function of infrastructure configuration, vehicle properties, timetable and delays for two crossing trains. The effect of possible surrounding trains is not taken into account and all kinds of congestion effects are thus excluded from evaluation. SAMFOST has been successfully validated against the simulation tool RailSys, which shows that this type of simplified model is accurate in non-congested situations.A great advantage of disregarding congested situations is that analysis is independent of timetable assumptions. The model also explicitly shows the effect of punctuality, which is of particular importance on single-track lines where the interdependencies between trains are strengthened by the crossings.For the same reason, the timetable is severely constrained. Nonetheless, there is often a need for changes of the timetable (crossing pattern). The thesis proposes three simple measures of timetable flexibility, all based on assigned crossing time requirements. Together, these measures can be used to evaluate how infrastructure configuration, vehicle properties, punctuality etc affect possibilities to alter the timetable.As an example of its application, SAMFOST has been used to evaluate the effect of shorter inter-station distance, partial double-track and combined crossing and passenger stop. These measures affect the operational properties quite differently.More crossing stations result in a minor decrease in travel time (lower mean crossing time) but significantly higher reliability (lower crossing time variance). These effects are independent of punctuality, which is a valuable property.A partial double-track results in shorter travel times and in some cases also higher reliability. Both effects are strongly dependent on punctuality and high punctuality is needed to achieve high effects.A combined crossing and passenger stop results in a situation similar to that of a partial double-track. In this case it is important to point out that the assignment of time supplements in the timetable should be directly correlated to punctuality in order to achieve good operation.