How Does Google Maps Know There's Traffic When You Can't See It?

Your Car Is Not Watching Traffic With A Camera Your navigation system doesn't need to see a line of stopped cars to know that traffic is moving slowly.

Google similarly says aggregate location data from people using Google Maps can be used to understand traffic conditions on roads around the world.

TomTom says its traffic-prediction system combines floating-car data with historical traffic information, including traffic flow, average speeds, travel times, and incident information.

Historical traffic data: Past driving patterns help establish what is normal for a particular road and time.

Another thread from the same subreddit noted that historical traffic data and mathematical models can help navigation services distinguish an ordinary slowdown from an unusual traffic jam.