13. A non-transitory machine-readable storage medium encoded with instructions that, when executed by one or more processors, cause the processor to carry out a process comprising: receiving a route request associated with a user; determining one or more candidate routes responsive to the route request, wherein each of the one or more candidate routes comprises one or more road segments; accessing a plurality of different road speed models, wherein each road speed model comprises a model of vehicle speeds on one or more of the one or more road segments during different conditions, each road speed model having been created by a road speed modeler configured to: collect observations of road speed data during a plurality of driving sessions, the road speed data including a set of sensor measurements relevant to road speed; and create the plurality of different road speed models corresponding to different conditions that impact the road speed; selecting at least one of the plurality of different road speed models based at least in part on one or more conditions associated with the route request; and employing the selected at least one road speed model to predict one or more travel times respectively for the one or more candidate routes.
20. The non-transitory machine-readable storage medium of claim 13 , wherein selecting at least one of the plurality of different road speed models based at least in part on one or more conditions associated with the route request comprises at least one selected from a group consisting of: determining a level of user hurriedness based on one or more detected driving behaviors; determining a current environmental condition; determining a current level of traffic; and determining a type of a road segment included in each candidate route.