Every wonder how Google Maps knows where/when there is traffic? by Walter McGee

Data is collected from various sources, dependent upon: 1) how urbanized the area is and 2) the nature of the street (ie, hwy, surface road, etc.).

Real-time Traffic Sources:

-Pole mounted radar

-Surface/Ground sensors

-Video cameras

-Cell phone GPS

These are usually found in urban or on high traffic throughways and often feed a city's traffic management system. This is provided or sold to a reseller (like NavTeq) and then to Google Maps.

Cell companies can pull velocity from your phone's GPS and/or cellular tower triangulation. Nearly all streets in the US are digitized and have defined speed limits. Cell phone data is generalized, the avg. velocity is calculated, and correlated to the speed limit on that road segment. Once a threshold is met (say 60% of the speed limit) for a certain amount of time, a line changes colour and is fed to any number of online mapping systems.

Walter McGee, Operations Planning Coordinator, GeoDigital International Inc.