Waze is a free iPhone app that does everything you expect a GPS navigation system to do.
That’s where the crowdsourcing features come in. Waze contains a menu where you can report a number of different events at your location: a traffic jam, a hazard in the road, an accident, or the presence of emergency vehicles, for example. When you report an event, the information is passed on to all other Waze users who approach the same area. The app even automatically redirects drivers on alternate routes to avoid reported traffic jams.