Google Maps can warn you about traffic before you reach it. But how does it know what is happening on a road you cannot even see?
You open Google Maps, enter a destination and suddenly see a road covered in red. Maps tells you that traffic is heavy and suggests another route.
It may seem like Google has a camera watching every road. In reality, Maps combines information from millions of journeys, GPS location data, road information and historical traffic patterns to build a picture of what is happening on the road.
Your Phone Helps Detect Traffic
One of the most important sources of traffic information is the movement of devices using Google Maps.
When people use navigation, Google can use aggregated location and navigation data to understand how vehicles are moving along roads. If multiple devices are moving slowly along the same stretch of road, Maps can detect that traffic is building up and use this information to estimate current traffic conditions.
If vehicles are moving normally, the road may remain green. When movement slows significantly, Maps can show the road in orange or red.
Google says navigation data can be used to provide real time traffic conditions, disruptions and faster route suggestions.
It Does Not Depend Only on GPS
GPS is important, but it is not the whole system.
Google can combine location information with navigation details and sensor data from devices. Google also uses information about roads and receives data from other sources, including authoritative information from local governments.
This gives Maps more information about what is happening on a particular road.
For example, if hundreds of devices are moving slowly through the same section of highway, that is a strong signal that something is causing a delay.
Maps Also Looks at the Past
Knowing what is happening right now is useful, but Google Maps also needs to estimate what will happen a few minutes from now.
This is where historical traffic patterns become important.
Google has years of information about how traffic normally behaves on different roads at different times. A road may be relatively clear early in the morning but become heavily congested during the evening rush hour.
Maps can combine these historical patterns with current traffic conditions to estimate how a journey is likely to develop. Google has described using machine learning to make these traffic predictions.
What About Accidents and Road Closures?
Traffic is not always caused by the usual morning or evening rush.
Accidents, construction, road closures, sporting events and other disruptions can suddenly change road conditions. Google Maps can display these types of disruptions and use available information to help drivers find alternative routes.
This is why the traffic information on your screen can change while you are already driving.
How Does Maps Know Which Route Is Faster?
Google Maps compares different possible routes using information about current and predicted traffic, road conditions and the structure of the roads.
If the system expects your original route to become slower, it can recommend an alternative. If conditions change during your journey, Maps can update the route again.
So when Maps says a different road will save you 10 minutes, that recommendation is based on much more than distance. It is an estimate built from current conditions, historical patterns and other available information.
The Simple Answer
Google Maps does not need to physically see every traffic jam.
It can understand traffic by combining GPS and location data, navigation information, device sensors, road information, historical traffic patterns and real time movement.
Millions of individual journeys become useful information about the roads around us.
The next time Google Maps tells you that traffic is waiting ahead, remember that your phone is not just showing you a map. It is helping build a live picture of how the road is moving.
