In today’s traffic, that will be more and more growing in the coming years, it is important for the individual as well as the public traffic to locate and navigate the vehicles. Therefore, systems have to be installed controlling the traffic and helping to find navigation solutions for the driver. But all these problems can only be solved if you know your exact location. One possibility is the use of DGPS. With it’s help you are able to get precise position data in real-time. In most cases it is sufficient to use corrected data. But for positioning with a very high accuracy, you have to use carrier phase observations. In the paper a precise positioning system to locate a vehicle by means of GPS carrier phases will be presented. With respect to the on-line aspect this will be one of the future methods in vehicle navigation. Further it is imaginable to use these systems for auto-pilot systems. Using DGPS to solve the problems of on-line positioning we have not to forget the real-time aspect of such a system. It is necessary to use algorithms which allow a fast and secure computation of the received data for ambiguity resolution and position determination.