GNSS-based Road User Charging (RUC) systems are particularly interesting because of their flexibility and reduced roadside infrastructure. At present, truck toll collection systems based on GPS receivers installed on the vehicles are already deployed in German and Slovak motorways. Reliability of road tolling systems is fundamental in order to limit the loss of revenue because of undercharging and the user claims because of overcharging. Consequently, GNSS integrity monitoring plays a key role in such systems, providing trustful positioning data that keep position errors and their associated legal or economical consequences within given limits. Nevertheless, the design of GNSS integrity algorithms like RAIM requires a deep knowledge of the characteristics of the application and GNSS errors. This paper analyzes the required parameters to develop RAIM algorithms for road tolling applications in urban and rural environments.