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. The paper describes the SIGNATURE solution and how it is being tested in the course of the project. It then presents initial results from field trials which are assessing its performance in a range of representative conditions. The tests assess the contribution that assistance can make to positioning performance, and illustrate options for enhancing standard assistance solutions. Enhancements to assistance encompass modifications to the message content and alternative means of communications, showing the benefits and feasibility of a broadcast service. The impact of including EGNOS corrections through a broadcast assistance service in urban areas is also under investigation.