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.
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. 16. The non-transitory machine-readable storage medium of claim 13 , wherein receiving a route request associated with a user comprises receiving a target destination, current time data and a current location of the user identified by one or more sensors.