A route engine can be configured to receive route data that characterizes a request for driving directions to a destination. The route engine can also be configured to determine a plurality of travel routes to the destination and to estimate a predicted travel time for each of the plurality of travel routes to the destination. The estimation can be based on environmental data that characterizes environmental conditions that affect traffic flow along the plurality of travel routes. The route engine can further include determining a likelihood that each predicted travel time for each of the plurality of travel routes is accurate.