I think you could get something almost as good by convincing Google to take traffic data into account when finding the least-cost route between two points. I know that in Chicago the freeways have speed sensors spaced pretty closely together, so it is possible to look at that data and immediately know how long you are going to spend on the freeway. If you use that data to determine your route, then you should avoid traffic jams.

Obviously conditions can change pretty quickly, but most of the time they don't. So this could be a good 90% solution without requiring people to broadcast their location to you.