Behaviors of road vehicles are highly affected by the road situations. The control units of the vehicles should know as more as possible information on the road to carry out proper operations. Positioning plus electronic map provides an access to get road information which is position dependent. Based on the traditional electronic map, the information of road layer, point layer and the subsidiary information are processed according to the requirements of real-time acquirements of road parameters. However, the traditional R/W mechanism of the subsidiary data of ordinary electronic maps can not satisfy the needs of real-time data acquirements. In order to avoid such situation mentioned above, the pre-reading mechanism is presented in this paper, which is to ensure real-time requirements. Test experiments run for the verification and validation, and the approach is proved to be effective and feasible.
