15. The computer-implemented method of claim 12 , 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.
15. The computer-implemented method of claim 12 , 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. 16. The computer-implemented method of claim 15 , 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.