A method of operating a navigation system for motor vehicles in which a location and a destination are entered through an input device and transmitted by mobile radio to a central navigation computer, and a travel route is transmitted to the mobile radio with inclusion of route network data and traffic-related additional information by the navigation computer, comprising the steps of: receiving the location, the destination and a desired arrival time at the input device; transmitting the location, the destination and the desired arrival time to the navigation computer; computing a trip starting time based on route network data and transportation traffic data; and outputting a trip start or wake-up call to one of (a) a mobile radio and (b) a telephone number for the purpose of communicating trip starting time for travel from the location to the destination.