A clarification of the terms reliability and robustness. More and more, reliability of travel times becomes an important issue. Policy plans are currently focusing on this issue. Several definitions and indicators for reliability can be found in literature. The problem is that these definitions and indicators are not always as clear as we would like them to be. In this paper we explain on which points the definitions and indicators must be improved in order to make them directly applicable. Further, little is known about the factors on which reliability depends. In particular, not much is known about the relationship between robustness of networks and reliability of travel times. This paper describes our point of view on reliability and all the factors that determine the reliability of travel times. Robustness is one of them. We go into more detail about the following aspects of robustness: redundancy, interdependency, resilience and flexibility. The meaning of these terms as well as their relevance for the robustness of networks is explained. We will also present some indicators which make it possible to measure these aspects of robustness. This is only a first attempt; further research on this subject is needed. (Author/publisher)
Samenvatting