GPS based navigation systems have been around for a number of years now. They typically receive signals from a satellite to find the current position, and then look up the map data (on your Palm, PocketPC, cell phone, laptop computer, or specific GPS device like Megellan/Garmin) to calculate the best way to route you to your destination.
However, the road condition keeps on changing, there could be accidents, construction, or traffic congestion ahead. If the GPS is simply looking up a computer database, they have no knowledge of what's going on ahead. This problem has been tackled recently by a few companies with "live" traffic conditions broadcasted to their GPS system. Typically they collect live traffic information from the transportation department or some local authority, and feed that data to the device. Another valuable information source is the tracking of cell phone signals on the road. These "live" traffic information services, not surprisingly, comes with a subscription fee. A simple search on the web reveals some of these new companies/products: Cobra, Pharos, TomTom, Teletype GPS, etc.
In future, it would be nice if the GPS device can collect and analyze the driving habit (such as average speed) of a driver on some typical roads or conditions, store them on a local device (to protect privacy), and automatically selects the best route for the driver based on the "live" traffic data, and his/her driving history. Also, as our local governments tackle the day-to-day traffic congestion problems, perhaps they will eventually be will to foot the bill for broadcasting the "live" traffic information, instead of relying on private companies that charge a subscription fee. After all, these traffic reports are free public information anyway.