Due to wireless communication technologies, positioning technologies and mobile computing develop quickly, mobile services are becoming practical and important on big spatiotemporal databases management. Mobile service users move only inside a spatial network, e.g. a road network. They often issue the K Nearest Neighbor (KNN) query to obtain data objects reachable through the road network. The challenge problem of mobile services is how to efficiently answer the data objects which user interest to the corresponding mobile users. Lu et al. have proposed a RNG (Road Network Grid) index for speeding up the KNN query on real-life road networks. Since they divide the road, this makes the number of points of the graph increase.