Joe:
Thanks for the suggestion. Navteq data does have an attribute associated with direction of travel ("B" for travel in both directions, "T" for travel in the "to" direction of the line, and "F" for travel in the "from" direction). The problem I have is, I can't be 100% certain that all northbound travel is in the "T" direction of the line, for example. The direction of the line may be counter to the listed direction of travel.
Bob