*4.2. Vehicle Low Traffic Density at Low Speed*

The second case of the proposed scheme involves low vehicle speed under low-traffic conditions. In this case, the virtual mix crowd method is used. The virtual crowd method scans the road environment for neighborhood vehicles in the surroundings, and based on the context of the vehicle neighbor's, the virtual pseudonym exchange process is executed. The target vehicle randomly selects one of the neighboring vehicles to exchange real and virtual pseudonyms with, as shown in Algorithm 4. Recall the beacon message include *BM*(*PID*, *Tx*, *V*, *NeighCount*, *D*, *DTresh*, *PUpdate*) and is used to sense the vehicle traffic environment. In the virtual pseudonym exchange scheme, the vehicle randomly selects one of the transmission range neighbors to exchange pseudonyms and update its *PUpdate* attribute. We discuss the virtual pseudonym exchange process with the help of an example. If vehicle *V*<sup>1</sup> wants to change the pseudonym and has *V*2, *V*3, *V*4, and *V*<sup>5</sup> in its neighbor list. *V*<sup>1</sup> will randomly select one of the vehicles and start an exchange of pseudonyms with *V*4. After completing the exchange process, both vehicles update their status of *PUpdate* and publish it to the vehicle's crowd. Each vehicle that exchanges pseudonyms must report to the CA the pseudonyms exchanged. This process will reduce the liability issue in the network. The vehicle generates an image of its real pseudonym and exchanges it with its neighboring vehicle. The receiving vehicle verifies both of these pseudonyms, accepts the real one, and rejects the fake pseudonym. The vehicle generates such an image of a pseudonym that it is difficult for an adversary to identify it. Similarly, other vehicles such as *V*2, *V*3, and *V*<sup>5</sup> also apply the virtual pseudonym exchange process in the vicinity. As many vehicles take part in the virtual pseudonym exchange process, this produces a virtual crowd of vehicles in the network, which mixes each vehicle identity and location in the crowd. The pseudonyms exchange process is shown in Figure 7.

**Figure 7.** Virtual pseudonym exchange process between two vehicles.
