There is a need to make the interface of Route Guidence systems more flexible, so that they can adapt to the specific driver needs. Today's systems are primarily aimed at tourists, and interfaces for drivers that have more experience of a city have not been investigated. In this paper we describe a study with very experienced driver-navigators, where we have deduced principles as to how route descriptions are constructed and expressed by humans. Some of these principles are implementable, and a rough outline of a program is presented. Given a plan of how to go to A to B in a city, the program produces a verbal description of that plan. The goal is to incorporate verbal descriptions in Route Guidence systems, primarily aimed at driver-navigators with some knowledge of the city.