This white paper, entitled “Better use of Global Navigation Satellite Systems for safer and greener transport”, explains the role of positioning systems in transportation and the necessity to correctly assess their performance. This document introduces the fundamentals of positioning systems with a particular focus on Global Navigation Satellite System (GNSS). It describes the positioning terminal architecture and the parameters used for the characterization of performance such as availability, accuracy and integrity. The goal of this white paper is to inform the key actors of the terrestrial transport sector on the issues and the impacts of positioning quality in applications, more specifically in intelligent transport systems.