MDKMDK wrote:
Most newer standalone GPS units have built in traffic updates. Ours worked well last trip out, over 7,000 miles round trip, with many traffic warnings near the bigger cities, and it automatically checks alternate routes for faster bypass. No cell signal required. Just traffic status on the satellites.
The traffic information is actually broadcast in side bands of terrestrial FM radio broadcasts, at least in the GPS units I'm familiar with.
The GPS satellites certainly do not broadcast anything resembling traffic data; their signals basically amount to very tightly synchronized clocks, with some satellite orbit positioning information encoded as well, and the GPS receiver determines the relative distance (based on the relative differences in time due to longer or shorter signal propagation paths) to each of the satellites it can pick up a signal from and uses that to triangulate its position. They can also compare the relative speed rate of the clocks due to doppler shifts and so determine relative velocity to the satellites, and since the satellites are not in geostationary orbit the whole three dimensional "where am I and how fast am I going" computation gets rather complicated....