Roads right across Europe are becoming more congested and governments and regional authorities are looking for ways to better manage the existing road network. One tool that is being increasingly promoted to tackle the congestion challenge is Road User Charging (RUC). Recording journey information using a GNSS receiver embedded in an OBU is a convenient and flexible solution to support the automated fee collection process. If GNSS positioning is to be used as the basis for billing drivers though it must meet stringent reliability and availability requirements, and at the same time, be based on low-cost equipment. This paper describes a prototype solution which has been developed to provide both the positioning availability and integrity required for this application. The SIGNATURE (SImple GNSS Assisted & TrUsted REceiver) solution includes an assistance service which provides ephemeris data and corrections from the EGNOS Data Access Service (EDAS), optimized for the user location. Assistance messages are sent to OBUs which can either host an experimental receiver or a Commercial-Off-The-Shelf (COTS) receiver. Measurement data from the receiver is then processed with application-specific navigation algorithms on the OBU which aim to improve the integrity of the position solution relative to standard solutions.