GraphHopper Routing Engine 0.7 Released

http://www.opentripplanner.org

I never really liked the waze method of manual input, but that's a really braindead way of getting started; it seems however that you could do tricks like anomaly detection of speed of a car through an area when compared to other cars on that street/streets around it with some very hand wavy heuristics. Contributors would install the app and it'd start building a database of avg speed and variance for roads/groups of roads. Anonimization comes to mind as a concern, but since you just need to know "someone drove on that street" at some point recently I imagine there are some things you can do to reduce potential impact/aggregate, since traffic jam data gets less useful in places with less people, although that does require a large starting population, and at this point I'm rambling.

The other advantage of a system like this is that it could readily be used for road discovery, frankly as someone who knows nothing about the open mapping community I always figured something like that _had_ to exist to make it more feasible.