Transport Infrastructure Slot Allocation

In this thesis, transport infrastructure slot allocation has been studied, focusing on selection slot allocation, i.e. on longer-term slot allocation decisions determining the traffic patterns served by infrastructure bottlenecks, rather than timetable-related slot allocation problems. The allocation of infrastructure capacity among carriers is a major issue in various transport infrastructure sectors, and therefore a theoretical framework on slot allocation would be desirable to support rational decision-making on slot allocation. The current state-of-the-art of slot allocation research does not provide such a theoretical framework, and therefore a theoretical framework to analyze slot allocation problems has been developed in this thesis. The first step in the development of a theoretical framework to analyze slot allocation problems has been the specification of a conceptual framework, which includes the definition of key concepts such as capacity. Capacity has been defined as being dependent on conditions such as composition of traffic and traffic context as well as assumptions about the desired balance between capacity and quality-of-service. The next step was to review the current application of slot allocation in the railway and aviation sectors, and the potential application of slot allocation in the road and navigation sectors. Slot allocation is currently applied in the railway and aviation sectors, and slot allocation may potentially be applied in other sectors. This thesis introduces the important distinction between selection and scheduling slot allocation. In both the railway and aviation sectors, the tradition has been to integrate selection and scheduling slot allocation. This thesis, however, considers selection slot allocation as a separate slot allocation level. Separating selection and scheduling slot allocation enables the application to each level of different rules with respect to slot validity, valuation of alternative slot requests, etc. The desired characteristics of selection slot allocation have been formulated in this thesis by analyzing the main desires of carriers and other interested parties such as shippers and authorities. It has been concluded that selection slots should be valid for a significantly longer period than scheduling slots, and a semi-static slot allocation procedure has been proposed. Furthermore, the acceptability principle has been introduced as a basis to specify desired slot size. However, the specification of standard basic slots by the allocation body (at different levels to attain differentiation of slot size) is desirable. A semi-static slot allocation procedure implies that selection slot allocation decisions may be based on an explicit evaluation of selection slot requests. The selection problem may be analyzed using congestion theory, resulting in a generic specification of traffic supply and demand. The next step is to specify traffic supply in more detail by specifying capacity constraints. Examining various types of primary traffic processes, traffic service processes, and traffic externalities, capacity constraints have been formulated, which may be applied to different types of bottlenecks. Three categories of capacity constraints have been distinguished, i.e. homogeneous capacity constraints, linear capacity constraints, and non-linear capacity constraints. The next step is the specification of objectives. The (primary) objective of slot allocation may usually be specified as a linear objective function. Depending on the type and number of capacity constraints, various instances of selection slot allocation decision problems may be formulated. The corresponding optimization problems may be solved using an exact solution algorithm, but for various reasons this thesis proposes a greedy approximation instead. Besides a standard greedy algorithm for selection problems with a single type of capacity constraint, an extended greedy algorithm has been developed to solve problems with two or more different types of capacity constraints. The latter algorithm has been tested for a hypothetical case study. Three main conclusions have been formulated in this thesis. The first main conclusion is that selection and scheduling should be considered as separate slot allocation levels having a hierarchical relationship. Selection slot allocation is of primary importance and scheduling slot allocation is only of secondary importance, because selection decisions determine which traffic is facilitated and which is not. The second main conclusion is that the validity of slots is a compromise between stability and flexibility. To ensure a sufficient level of stability, a validity of at least 5 years seems reasonable for selection slots. To ensure a reasonable level of flexibility, infinite validity of selection slots (historic rights) is not desirable, and at least every timetable season the opportunity should be offered to reserve selection slots. The final main conclusion is that the objec-tives and constraints of the selection problem can be modeled as linear functions, and the resulting binary linear programming problem can best be solved with the greedy efficiency algorithm presented in this thesis. This efficiency algorithm does not provide an exact solution of the binary linear programming problem, but its results are more robust and are easier to interpret than exact solution approaches.