Safety-critical and liability-critical GNSS-based applications are needed to enable Intelligent Transport Systems and smart mobility. This requires trusted GNSS signals that are authenticated and of appropriate integrity. Assessing GNSS signal integrity in complex urban environments is not easy, but the GLOVE FP7 project has successfully demonstrated one possible approach that uses inter-vehicle communication to collate information on GNSS signal quality from a number of vehicles for assessing the local integrity.