Google Maps: the fastest route on roads that keep changing

How directions, live traffic and the map work for 2 billion monthly users: a road graph partitioned once into cells with a shortcut overlay whose costs are re-customized from live speeds in under a second, phone fixes map-matched into per-segment speeds within about two minutes, arrival times that time each road for when the driver reaches it, and vector tiles named by quadkey under immutable, versioned URLs.