[NateEag]

It would be hard, yeah.

It's a network effect thing - if enough people used an OSM client and opted into sharing anonymized location data, you might be able to get somewhere with it.

In practice, I think it'd have the same problem as the core map data - surprisingly good data in places with a lot of adopters, and nothing at all in places without.

That said, though, the traffic data is pretty secondary - a good, open routing engine would be lovely to have, and will slowly become more relevant as the map expand and fills out.