6. The non-transitory machine-readable storage medium of claim 1 , wherein assigning a default value for one or more unseen road segments comprises computing a summary statistic for one or more unseen road segments, the summary statistic assigning a statistically estimated attribute value for each unseen road segment.
6. The non-transitory machine-readable storage medium of claim 1 , wherein assigning a default value for one or more unseen road segments comprises computing a summary statistic for one or more unseen road segments, the summary statistic assigning a statistically estimated attribute value for each unseen road segment. 7. The non-transitory machine-readable storage medium of claim 6 , wherein computing a summary statistic for an unseen road segment comprises determining a mean or median attribute value observed in other driving sessions for the unseen road segment.