Due to the progress of modern automobiles, using vehicles as sensors to gather information is no longer an unreachable idea. Although the cost of providing services on a specific node is extremely high in Mobile Ad Hoc Network (MANets), to locate a particular node and provide services in Vehicular Ad-hoc Network (VANets) is much easier than in MANets because vehicles are always limited on roads. Particularly, public transportation systems are very suitable for providing Web services. In our approach, we purpose a geo-aware tree-based service tracking scheme to locate the specific service in the particular area. The virtual backbone is predefined according to the main roads in the city. It consists of geo-grids and is further organized to a tree structure. The tree structure, which is the higher layer of the virtual backbone, can be used to facilitate service location tracking since any grid inside the tree has only one route to the root. Based on footprints left by services on the branches of tree, we can easily find the specific service and access data of interests on VANets. The footprints will be updated when the service move from one grid to another or be cleared when the service jump into another branch of the tree structure.