Railway scheduling reduces the expected project makespan.

The Critical Chain Scheduling and Buffer Management (CC/BM) methodology, proposed by Goldratt (1997), introduced the concepts of feeding buffers, project buffers and resource buffers as well as the roadrunner mentality. This last concept, in which activities are started as soon as possible, was introduced in order to speed up projects by taking advantage of predecessors finishing early. Later on, the railway scheduling concept of never starting activities earlier than planned was introduced as a way to increase the stability of the project, typically at the cost of an increase in the expected project makespan. In this paper, we will indicate a realistic situation in which railway scheduling improves both the stability and the expected project makespan over roadrunner scheduling.Railway scheduling; Roadrunner scheduling; Feeding buffer; Priority list; Resource availability;

Project management under uncertainty: a study on solution methods

Project Management involves onetime endeavors that demand for getting it right the first time. On the other hand, project scheduling, being one of the most modeled project management process stages, still faces a wide gap from theory to practice. Demanding computational models and their consequent call for simplification, divert the implementation of such models in project management tools from the actual day to day project management process. Special focus is being made to the robustness of the generated project schedules facing the omnipresence of uncertainty. An "easy" way out is to add, more or less cleverly calculated, time buffers that always result in project duration increase and correspondingly, in cost. A better approach to deal with uncertainty seems to be to explore slack that might be present in a given project schedule, a fortiori when a non-optimal schedule is used. The combination of such approach to recent advances in modeling resource allocation and scheduling techniques to cope with the increasing flexibility in resources, as can be expressed in "Flexible Resource Constraint Project Scheduling Problem" (FRCPSP) formulations, should be a promising line of research to generate more adequate project management tools. In reality, this approach has been frequently used, by project managers in an ad-hoc way

Project management under uncertainty: Solution methods revisited

Project Management involves onetime endeavors that demand for getting it right the first time. On the other hand, project scheduling, being one of the most modeled project management process stages, still faces a wide gap from theory to practice. Demanding computational models and their consequent call for simplification, divert the implementation of such models in project management tools from the actual day to day project management process. Special focus is being made to the robustness of the generated project schedules facing the omnipresence of uncertainty. An "easy" way out is to add, more or less cleverly calculated, time buffers that always result in project duration increase and correspondingly, an increase in its cost. A better approach to deal with uncertainty seems to be to explore slack that might be present in a given project schedule especially when a non-optimal schedule is used. The combination of such approach to recent advances in modeling resource allocation and scheduling techniques to cope with the increasing flexibility in resources, as can be expressed in "Flexible Resource Constraint Project Scheduling Problem" (FRCPSP) formulations, should be a promising line of research to generate more adequate project management tools. In reality this approach is frequently used by project managers in an ad-hoc way

Project scheduling under undertainty – survey and research potentials.

The vast majority of the research efforts in project scheduling assume complete information about the scheduling problem to be solved and a static deterministic environment within which the pre-computed baseline schedule will be executed. However, in the real world, project activities are subject to considerable uncertainty, that is gradually resolved during project execution. In this survey we review the fundamental approaches for scheduling under uncertainty: reactive scheduling, stochastic project scheduling, stochastic GERT network scheduling, fuzzy project scheduling, robust (proactive) scheduling and sensitivity analysis. We discuss the potentials of these approaches for scheduling projects under uncertainty.Management; Project management; Robustness; Scheduling; Stability;

Proactive-reactive procedures for robust project scheduling.

The vast majority of research efforts in project scheduling concentrates on developing procedures to generate workable baseline schedules that minimize the project makespan in a deterministic environment. However, a real-life project is inevitably subject to uncertainty during execution. This dissertation aims at introducing procedures that cope with disruptions during execution. We limit ourselves to the treatment of time uncertainties caused by the fact that actually realized activity durations during project execution may deviate from the expected activity durations. When dealing with uncertainty in a scheduling environment, there are, generally spoken, two main approaches. Proactive scheduling focuses at incorporating safety in the schedule to absorb future disruptions, while reactive scheduling denotes how to react when a disruption occurs. Both approaches are inescapably related. We will investigate in how several proactive-reactive scheduling decisions can help a project manager to increase the quality of a project. The text of this dissertation is organized as follows. Chapter 1 introduces the problem of proactive-reactive project scheduling and situates it in the extensive project scheduling literature. Chapter 2 formulates the problem at hand and defines the concepts required in the remainder of the thesis. The trade-off between makespan and stability in project scheduling of Chapter 3 justifies the research efforts made in Chapters 4, 5 and 6 to add safety to the baseline schedule. Mainly two approaches to add safety are discussed in this thesis. First, a schedule is made proactive in Chapter 4 by deciding how the resources flow throughout the project. Next in Chapter 5, we develop efficient and effective procedures to add idle time (buffers) into a schedule to anticipate unforeseen events. Chapter 6 contains an extension of Chapters 4 and 5 by merging scheduling, resource allocation and buffer allocation decisions into an integrated approach. The reactive procedures that are required to decide how to react on disruptions that cannot be absorbed by the baseline schedule are introduced in Chapter 7. In Chapter 8 an extensive simulation-based experiment is set-up to evaluate several predictive-reactive resource-constrained project scheduling procedures proposed in the previous chapters. Chapter 9 applies the proactive-reactive project scheduling methodology on a real-life project that stems from our experience in the Belgian construction industry. Accordingly, a risk management framework is introduced to detect and analyze the risks that constitute the uncertainty implied in the project. In a last chapter, some overall conclusions and recommendations are provided.

Simulation and Control of Groups of People in Multi-modal Mobility

Tourism and transport are constantly growing and, with it, the movements of travellers. This entails two fundamental effects on which we must focus: control of mass tourism and the organization of transport. Good transport organization and travel planning avoid crowds and therefore mass tourism. This allows promoting sustainable tourism in which it is sought to offer a quality service to tourists taking care of the environment. In this thesis the objective is to manage the flow of groups of people through means of transport. This control of groups of people is aimed at customer satisfaction by offering quality tourism. On the one hand, the study focuses on the problem to mitigate the negative effects due to mass arrivals in touristic locations. A TEN network has been developed to define the optimal tours for different groups of tourists. A related mixed integer quadratic optimization model has been developed with three main objectives: it minimizes the maximum value of occupancy in the selected destinations to limit mass tourism, reduces the divergence between the proposed visit tour and one required by the tourist group and the overall duration of their visit, and a heuristic approach has been introduced. On the other hand, it has been implemented a railway scheduling and rescheduling problem introducing optimization-based and min-max approaches on the regional and high-speed railway network. The scheduling model defines the best schedules for a set of trains considering costumers\u2019 demand and the priority of the trains to cover the rail sections in case of conflict on the railway lines. Consecutively, the generated feasible timetables are used to minimize possible consequences due to events that may negatively affect the real time traffic management. The main contribution of this section is the introduction in the second approach the innovative concept to prioritize the train that can access on the block section in case of conflicts on the network