A route-planning system is described that leverages a database of observations about routes taken by drivers in a region to generate context and/or preference sensitive routes. Contextual information such as time of day and day of week, along with such findings as the observed velocities on different roads and the efficiency of trips is noted from the database of trips to inform a route generation component. The route-generation component considers velocities, contextual information, and other findings to compute preferred routes for people requesting directions from a first geographical point to a second geographical point. In one usage, properties of a driver's own prior routes are used to generate personalized routes, including routes between previously unobserved starting and ending locations. In another application, sets of observed routes of other drivers are used in a collaborative manner to generate recommended routes for a specific driver based on inferred preferences of the driver.