For offline navigation there is data, the OpenStreetMap, for most places on the planet. There is no very good app though, which would have seemed to be the smaller problem.

For real time navigation, Waze type solution could work -- aggregation of real time data from users. Also, smart city projects have open traffic data APIs, although not sure wether there is something properly real time, or it something like hourly aggregates.

So that would be still a giant project, but data does not seem to be the bottleneck.