Originally Posted by RickO
That's interesting. How does it get real time information without an internet connection????
To incorporate data about ever-changing traffic and road conditions, however, GPS units must be able to receive live information over the air. One way to do this is by radio transmissions over frequencies that are close to the frequencies used by your car stereo. By using "sidebands" or the Radio Data Service (RDS), providers such as MSN Direct and Navteq send digitized traffic (and often weather and news) information to equipped GPS units from local radio transmitters.
Cars with built-in Sirius/XM satellite radio and GPS systems can also receive live traffic information in the background over the satellite radio signal. This information will be automatically incorporated into the GPS system's route.
These services usually require a subscription. The above systems are also "one-way:" while the mobile GPS unit receives data from the traffic information source, it doesn't communicate any information back.
Source: How Does Live Traffic on GPS Work? | eHow.com
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