Towards intelligent transportation Cyber-Physical Systems: Real-time computing and communications perspectives Traffic accidents and congestion problems continue to worsen worldwide. Because of vast number of vehicles manufactured and sold every year transportation sector is significantly stressed, leading to more accidents and fatalities, and adverse environmental and economic impact. Efforts across the world for Smart Transportation Cyber Physical Systems (CPS) are aimed at addressing a range of problems including reducing traffic accidents, decreasing congestion, reducing fuel consumption, reducing time spent on traffic jams, and improve transportation safety. Thus, smart transportation CPS is expected to contribute a main role in the design and development of intelligent transportation systems. The advances in embedded systems, wireless communications and sensor networksprovides the opportunities to bridge the physical components and processes with the cyber world that leading to a Cyber Physical Systems (CPS). Feedback for control through wireless communication in transportation CPS is one of the major components for both safety and infotainment applications where vehicles exchange information using vehicle-to-vehicle (V2V) through vehicular ad hoc network(VANET) and/or vehicle-to-roadside (V2R) communications. For wireless communication IEEE has 802.11p standard for Dedicated Short Range Communication (DSRC) for Wireless Access forVehicular Environment (WAVE). In this paper, we present how different parameters (e.g., sensing time, association time, number for vehicles, relative speed of vehicles, overlap transmission range, etc.) affect communication in smart transportation CPS. Furthermore, we also present driving components, current trends, challenges, and future directions for transportation CPS.