# How does my GPS know that there is traffic ahead? **URL:** \ **Category:** Factual Questions\ **Created:** [September 5, 2012, 2:14pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747 "2012-09-05T14:14:33Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![bizerta](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@bizerta](https://boards.straightdope.com/u/bizerta)\ **Post date:** [September 5, 2012, 2:14pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/1 "2012-09-05T14:14:33Z")
For that matter, when my Boston TV stations do traffic reports, their map shows where the slowdowns are by showing green (no slowdown), yellow (moderate slowdown), or red (severe slowdown). Where do they get such information in what-appears-to-be real time? Some possibilities: (A) those metallic sensors in the roadway. I would think this would require hundreds, if not thousands, of these in the greater BOS area. (B) Cell phones. Cell phones are constantly emitting signals. Are cell phone companies tracking moving cell phone velocity/locations (BigBrother, eat your heart out). © a plethora of cameras pointed at major traffic arteries. That would require someone monitoring them all and entering the data on a continuous basis. ---
**Author:** ![Peremensoe](https://avatars.discourse-cdn.com/v4/letter/p/ce7236/32.png) [@Peremensoe](https://boards.straightdope.com/u/Peremensoe)\ **Post date:** [September 5, 2012, 2:33pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/2 "2012-09-05T14:33:02Z")
There are road sensors and/or traffic cameras in some areas. Then there are reports from police (crashes) and transportation departments (road work). ---
**Author:** ![Jas09](https://avatars.discourse-cdn.com/v4/letter/j/d07c76/32.png) [@Jas09](https://boards.straightdope.com/u/Jas09)\ **Post date:** [September 5, 2012, 2:37pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/3 "2012-09-05T14:37:18Z")
Yeah, as I understand it there are two parts to the system: the inputs (which can vary by location) and the information distribution (which is how your GPS nows about). Localities can generate traffic data in many different ways, upload it to the traffic monitoring system, and then your GPS receives the information for it’s current location. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [September 5, 2012, 2:54pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/4 "2012-09-05T14:54:42Z")
(B) is actually going to be the case soon: apparently iOS 6 (which ships next week) will include [anonymous, crowd-sourced traffic info](http://applenapps.com/special-event/ios-6-new-maps-with-navigation-crowd-sourced-traffic-3d-view.html). I assume it will be opt-in; if you do, your phone would report its location and speed to some centralized server. Most likely this would be done using GPS, as I don’t think a cell phone signal alone would provide enough location precision. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [September 5, 2012, 4:39pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/5 "2012-09-05T16:39:00Z")
GPS is God’s Positioning System. people were getting in traffic jams and cussing and swearing and road rage. telling people to ‘love your neighbor’ wasn’t working here. god then intervened and is sending data direct to you to help keep you peaceful. road sensors and cameras are monitored by government transportation agencies. they compile this information and send it out in real time. some GPS units also get land based radio signals which has this real time local traffic data. ---
**Author:** ![Son\_of\_a\_Rich](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/son_of_a_rich/32/5439_2.png) [@Son\_of\_a\_Rich](https://boards.straightdope.com/u/Son_of_a_Rich)\ **Post date:** [September 5, 2012, 4:55pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/6 "2012-09-05T16:55:07Z")
This is no shit: I once had a boss who asked me how the GPS satellites kept track of all those cars. ---
**Author:** ![suranyi](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@suranyi](https://boards.straightdope.com/u/suranyi)\ **Post date:** [September 5, 2012, 5:13pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/7 "2012-09-05T17:13:03Z")
> [@Jas09](#): > > Yeah, as I understand it there are two parts to the system: the inputs (which can vary by location) and the information distribution (which is how your GPS nows about). Localities can generate traffic data in many different ways, upload it to the traffic monitoring system, and then your GPS receives the information for it’s current location. For some information about one popular method of information distribution, see this Wikipedia page on the [Traffic message channel](http://en.wikipedia.org/wiki/Traffic_message_channel)(TMC). ---
**Author:** ![bup](https://avatars.discourse-cdn.com/v4/letter/b/6bbea6/32.png) [@bup](https://boards.straightdope.com/u/bup)\ **Post date:** [September 5, 2012, 6:29pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/8 "2012-09-05T18:29:46Z")
> [@Son\_of\_a\_Rich](#): > > This is no shit: I once had a boss who asked me how the GPS satellites kept track of all those cars. A lot of people can’t get their heads around the idea that the satellite doesn’t know your device exists. They think the satellite is telling you your position. ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [September 5, 2012, 6:32pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/9 "2012-09-05T18:32:59Z")
So, **Son of a Rich** should have asked his boss how all those radio stations can keep track of all those radios all over the world. There must be millions! And that’s not even counting ones in cars! AM _and_ FM! And shortwave! ---
**Author:** ![gazpacho](https://avatars.discourse-cdn.com/v4/letter/g/6f9a4e/32.png) [@gazpacho](https://boards.straightdope.com/u/gazpacho)\ **Post date:** [September 5, 2012, 7:03pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/10 "2012-09-05T19:03:12Z")
> [@Acsenray](#): > > So, **Son of a Rich** should have asked his boss how all those radio stations can keep track of all those radios all over the world. There must be millions! And that’s not even counting ones in cars! AM _and_ FM! And shortwave! They outsource that to the ratings agencies. ---
**Author:** ![Digital\_is\_the\_new\_Analog](https://avatars.discourse-cdn.com/v4/letter/d/a88e4f/32.png) [@Digital\_is\_the\_new\_Analog](https://boards.straightdope.com/u/Digital_is_the_new_Analog)\ **Post date:** [September 7, 2012, 2:12am UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/11 "2012-09-07T02:12:06Z")
> [@MikeS](#): > > (B) is actually going to be the case soon: apparently iOS 6 (which ships next week) will include [anonymous, crowd-sourced traffic info](http://applenapps.com/special-event/ios-6-new-maps-with-navigation-crowd-sourced-traffic-3d-view.html). I assume it will be opt-in; if you do, your phone would report its location and speed to some centralized server. Most likely this would be done using GPS, as I don’t think a cell phone signal alone would provide enough location precision. [Apparently, Google was “Crowdsourcing road congestion data” in 2009.](http://googleblog.blogspot.com/2009/08/bright-side-of-sitting-in-traffic.html) -D/a ---
**Author:** ![control-z](https://avatars.discourse-cdn.com/v4/letter/c/eada6e/32.png) [@control-z](https://boards.straightdope.com/u/control-z)\ **Post date:** [September 7, 2012, 3:55pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/12 "2012-09-07T15:55:45Z")
[It gets traffic info from FM radio signals.](http://www.ehow.com/facts_7476284_gps-fm-traffic-work.html) ---
**Author:** ![suranyi](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@suranyi](https://boards.straightdope.com/u/suranyi)\ **Post date:** [September 7, 2012, 5:29pm UTC](https://boards.straightdope.com/t/how-does-my-gps-know-that-there-is-traffic-ahead/633747/13 "2012-09-07T17:29:49Z")
> [@control-z](#): > > [It gets traffic info from FM radio signals.](http://www.ehow.com/facts_7476284_gps-fm-traffic-work.html) Yes, that system is the Traffic Message Channel, which I mentioned in my post, and which is discussed in more detail in that Wikipedia page I cited.