1. A method for a computing system to facilitate navigation of roads by vehicles based on predicted traffic congestion of the roads, the method comprising: receiving information describing a network of roads in a geographic area; for each of the roads in the network, identifying multiple segments of the road for which traffic congestion will be distinctly tracked; and facilitating navigation of vehicles over the network of roads based on predicted traffic congestion of the roads by, for each of multiple users, receiving a request from the user for information indicating predicted traffic conditions of roads of the network for travel to an indicated destination; receiving information indicating current conditions that affect future traffic on the roads in the network, the current conditions including current levels of traffic on the roads, current weather for the geographic area, current events that are scheduled to occur in the geographic area, and current school sessions that are scheduled to occur in the geographic area; identifying segments of roads of the network along one or more routes to the indicated destination from at least one possible starting position, each of the one or more routes including multiple identified road segments; for each of multiple distinct future times, predicting an expected level of traffic congestion for each of the identified road segments at that future time, the predicting being based at least in part on the indicated current conditions; for each of the one or more routes, determining a predicted travel time for the route based on the predicted expected traffic congestion levels for the multiple road segments of the route, the determining such that at least one predicted expected level of traffic congestion at a first future time is used for a first group of one or more of the road segments of the route and such that at least one predicted expected level of traffic congestion at a second future time is used for a second group of one or more other of the road segments of the route, the second future time being later than the first future time and the road segments of the second group being after the road segments of the first group along the route; and providing information to the user that indicates the determined predicted travel time for at least one of the routes to the indicated destination, so that users can navigate vehicles over the network of roads based on predicted traffic congestion of the roads at multiple future times.