In this work, we present a comparative study of two strategies for opportunistic vehicular access over TV White Spaces (TVWS) spectrum, in the presence of fixed secondary networks. When the vehicular network meets other opportunistic users in the same TVWS channel, the first strategy is searching for a TVWS channel for exclusive vehicular access, while the other approach explores the coexistence between the vehicular network and the fixed secondary network. To carry out the evaluation of the strategies, we use the NS-3 network simulator, including some of the cognitive radio modules developed. Results showed that, in the case of study, the strategy of coexistence between the vehicular network and other opportunistic users over the TVWS channel (i.e., sharing the same TV channel) reduces the average access channel delay up to 15% and the average packet loss up to 17%.