6.2.3. Vehicle Traceability

Traceability is another privacy metric that measures the tracking percentage of vehicles during a trip. It is inverse to the level of location privacy. It is the probability of an adversary determining the location spots of the vehicles. Let *T<sup>v</sup>* be the tracing probability of an attacker itself, a measure of anonymity set. Traceability can be defined as given below [42]:

$$T\_v = [1 - Pr(|ASS|)].\tag{26}$$

*Pr* is the probability of vehicle anonymisation during the pseudonym change process. The value of *T<sup>v</sup>* equal to 1 means that the adversary successfully tracked the target vehicle by linking its various pseudonym during various location spots. With increasing anonymisation, the traceability strength of an adversary reduces over time.
