GPS navigators have been widely adopted by drivers. However, due to the sensibility of GPS signals to terrain, vehicles cannot get their locations when they are inside a tunnel or on a road surrounded by high-rises where the satellite signal is blocked. This incurs the safety and convenience problems. To address the issue, we propose a novel Grid-based On-road localizaTion system (GOT), where vehicles with or without accurate GPS signals self-organize into a vehicular ad hoc network (VANET), exchange location and distance information and help each other to calculate an accurate position for all the vehicles inside the network. GOT uniquely evaluates some fuzzy geometric relationship among vehicles and employs a grid-based approach to calculate vehicle's locations, by which GOT solves the issues of lack of beacon nodes and error propagation that are the two major challenges in on-road localization. Simulation shows our GOT system is very effective and efficient in calculating the vehicular positions.