This book constitutes the refereed proceedings of the 16th International Workshop on Communication Technologies for Vehicles, Nets4Cars/Nets4Trains/Nets4Aircraft 2021, held in Madrid, Spain, in November 2021. The 6 full and 2 short papers were carefully reviewed and selected from numerous submissions. The selected papers present original research results in areas related to the physical layer, communication protocols and standards, mobility and traffic models, experimental and field operational testing, and performance analysis