At present, many detectors installed on both urban and interurban roads are capable of extracting information from vehicles such as speed, length or direction of traffic. However, very few sensors are currently able to communicate and exchange information with vehicles in real time. For this reason and due to the existing need for vehicle-infrastructure communication in Intelligent Transportation Systems (ITS), this paper proposes the use of Radio-Frequency-Identification cards together with the magnetic loops already in operation on the road to extract and exchange information about different vehicles through bidirectional communication. This usage will lead to many applications. Therefore, different RFID cards and their operating mode and the electrical circuits necessary for accurate system operation will be presented and analyzed.