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.
Its an issue. But if all the code is open and audited, there should be a way to ensure only aggregates are used, and the reports are anonymous. There would also be a related issue of bot accounts who would try to sabotage the statistics for fun, but should also be reasonably solvable.
I still wouldn't provide that data for two reasons. Firstly, all the assurances in the world aren't going to convince me that there's no risk in transmitting my location to a random computer in the cloud. I'm not going to personally comb through an open source project to make sure my data is not being abused. I would have to ' trust' strangers that it is not. And if I'm trusting strangers with my location data well then we're back to square one.
Secondly, and this is really a different issue and perhaps not that widespread, I don't like turning on location on my devices simply because it reduces battery life. It's not a privacy issue but it's another roadblock (pun not intended) to gathering navigation data
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.