1. This is largely country-dependent with some governments being quite adamant that address data should be in the public domain, and some governments doing the opposite and selling address databases to private companies for some quick cash, where private companies then sell address lookups for some absurd per-lookup price for the next few decades. Most of the world though is probably just not rich enough to compile, publish and accurately maintain a national address database.
OpenAddresses is perhaps the gold standard for open source address data compilation from government datasets. Note for the future that alltheplaces.xyz (project I contribute to) is looking like it may eventually perform the automatic address data download/extraction/compilation that OpenAddresses currently performs. This has the benefit that in backwards countries, alltheplaces.xyz also obtains some addresses through other means--such as advertised location of international restaurant chains. And quite often, being within +/- 100 address numbers on a road is good enough for navigation. Google Maps obviously crawls addresses from all over the Internet AND has quite a high tolerance for errors, hence will perhaps always seem more complete than OSM.
2. Some further ideas for open source mapping applications trying to determine real time traffic situations:
2a. Use GTFS/GTFS-RT feeds for bus networks to detect real time delays but also to compare planned bus route schedules for different times of the day (different traffic conditions) where buses share the road with the public. There's already a few maps out there that overlay nearby GTFS-RT feeds for the city of interest and usefully provide a visual indication of how well public transport vehicles are currently moving.
2b. alltheplaces.xyz extracts public traffic camera feeds which could be presented to users when they plan/commence a journey as an indication of what lies ahead on the route.