Ever wondered how Google Maps knows a traffic jam is looming - even before you’re stuck in it? The answer lies in three powerful ingredients. First, millions of smartphones running Google Maps send anonymised location and speed data to Google’s servers. When many devices slow down together, the system flags congestion in real time. 

Second, Google layers in vast stores of historical traffic information - how fast cars normally move on a given road during specific times and days. This enables the app to not only show traffic NOW, but also predict what it’ll look like in 10, 20 or 50 minutes. 

Third, machine-learning models (including graph neural networks) analyse both real-time and historical data, factoring in events like accidents, construction or weather disruptions to recommend better routes. 
In sum: by blending live and past data with predictive analytics, Google Maps enables you to avoid slow-downs, pick smarter routes and reach faster - often before the jam has fully formed.