GNSS-based Road User Charging (RUC) systems have recently attracted special attention because of their flexibility and reduced roadside infrastructure. For instance, German and Slovak motorways already perform truck toll collection by means of GPS receivers installed on the vehicles. Road toll belongs to the so-called liability critical applications, which are characterized by the fact that they must use trustful positioning data in order to control the navigation errors and their negative legal or economical consequences. Consequently, integrity monitoring of GNSS signals plays a key role in such systems. Nevertheless, the design of GNSS integrity algorithms like RAIM requires a deep knowledge of the characteristics of the application, the received signals and the environment effects on them. This paper analyzes and provides the required parameters to develop RAIM algorithms for road tolling applications in urban and rural environnements.