We consider in-band full-duplex (FD) vehicular access networks in which a FD vehicular access point (AP) with high mobility simultaneously supports half-duplex (HD) downlink and uplink users with low mobility. We assume no self-interference due to FD operation at the AP and no channel state information known at the transmit side (no channel state information at the transmitter side). We completely characterize the sum degrees of freedom (DoF) by proposing an optimal blind interference alignment scheme, which exploits the difference of channel's temporal correlations between the AP and users, and establishing the matching upper bound on the sum DoF. Performance evaluation shows that the proposed scheme improves the sum rate at the finite signal-to-noise ratio regime compared to the conventional HD system.