We propose a cyber-physical platform that combines road traffic simulation, network simulation, and physical vehicles to facilitate extensive testing on various levels of vehicular systems. Our design integrates physical and digital vehicles into a common development and testing environment. This paper describes the platform design and presents prototypical implementations that use SUMO, TOSSIM, a 3D sensor simulation environment, and a test-bed of miniature vehicles called Gulliver. As a prototypical implementation, we demonstrate the development of cooperative applications, and by that we achieve: (a) a cyber-physical system that provides a common environment for physical and digital vehicles, (b) a platform to interface communication between physical and digital vehicles, and (c) the ability to tailor testing scenarios in which some system components are simulated digitally and some physically. The suggested design provides flexibility, cost efficiency, and scalable testing opportunities for future vehicular systems. Furthermore, the pro- posed system is able to support novel steps towards intelligent transportation systems for smart cities.