This book constitutes the joint refereed proceedings of the Third International Workshop on Communication Technologies for Vehicles, Nets4Cars 2011and the First International Workshop on Communication Technologies for Vehicles in the Railway Transportation, Nets4Trains 2011, held in Oberpfaffenhofen, Germany, in March 2011. The 7 full papers of the rail track and 12 full papers of the road track presented together with a keynote were carefully reviewed and selected from 13 and 21 submissions respectively. They provide an overview over the latest technologies and research in the field of intra- and inter-vehicle communication and present original research results in areas relating to communication protocols and standards, mobility and traffic models, experimental and field operational testing, and performance analysis.