To date, many vehicular ad hoc network unicast routing protocols have been proposed to support efficient packet transmission between vehicles in urban environments. However, when there is insufficient vehicle density during non-rush hour times, the vehicular ad hoc network is often intermittently connected. These unicast routing protocols, therefore, perform poorly when forwarding packets over this vehicular disruption tolerant network. This paper adopts the controlled replication approach, in a proposed IG-Ferry routing protocol, to spray a limited number of packet copies, denoted by packet token values, to relay vehicles in a vehicular disruption tolerant network. We then identify three kinds of relay vehicle, i.e. direct buses, non-direct buses and private cars according to their travel itineraries. Based on the proposed delay evaluation function for the three types of intermediate vehicle, the IG-Ferry packet spraying mechanism, instead of that of traditional binary spraying, can efficiently spray appropriate packet tokens to vehicles. Finally, intensive NS2 simulations are conducted using the realistic Shanghai city vehicle traffic trace, IEEE 802.11p protocol, with EDCA and the Nakagami radio propagation model, to show that IG-Ferry outperforms three well-known VDTN routing protocols, in terms of average packet delivery ratios, end-to-end transmission delays and packet replication overheads, with respect to various combinations of five communication parameters.