How Self-Driving Cars Think

Mapping, Scanning, Anticipating & Responding

At the most basic level, a self-driving vehicle needs to be able to answer four basic questions:

  • Where am I?
  • What’s around me?
  • What will happen next?
  • What should I do?

Where am I? (Mapping)

Waymo’s detailed, pre-built 3D maps highlight information such as curbs and sidewalks, lane markers, crosswalks, traffic lights, stop signs, and other road features. They also include knowledge of state and local traffic laws and regulations. Together with real-time sensor data, Waymo can precisely determine its location on the road and operate safely. Learn more about how Waymo creates maps for its vehicles.

What's around me? (Scanning)

Waymo is constantly scanning for objects around the vehicle—pedestrians, cyclists, vehicles, road work, obstructions—and continuously reading traffic controls, from traffic light color and railroad crossing gates to temporary stop signs. Waymo can see up to 300 meters away (nearly three football fields) in every direction.

Waymo can identify and differentiate other road users (e.g., cars, motorcycles, cyclists). It also knows what different colors mean when it comes to static objects such as traffic signals. These abilities help Waymo understand the situation around the vehicle—whether a light is green and clear for the vehicle to proceed, or whether a lane is blocked because of the many cones in front of it.

What will happen next? (Anticipating)

Waymo’s software understands that, for example, though pedestrians, cyclists, and motorcyclists may look similar, their behavior can vary dramatically. Pedestrians move more slowly than either cyclists or motorcyclists, but they can change direction more suddenly. Through real-world driving experience, simulation, and closed-course testing, Waymo is constantly learning and improving its understanding of how different road users are likely to behave and anticipate what they will do next.

Waymo also takes into account how changing road conditions (such as a blocked lane up ahead) may impact how other road users behave.

Self-driving vehicle on the road

What should I do? (Responding)

Waymo considers all of this information to determine the precise direction, speed, and steering maneuvers needed for the vehicle to progress along its route safely. Waymo’s baked-in defensive driving behaviors, such as staying out of other drivers’ blind spots and leaving extra room for cyclists and pedestrians, keep its passengers and other road users safe.

Because Waymo is constantly monitoring the environment and predicting the future behavior of other road users 360 degrees around the vehicle, it can respond quickly and safely to changes on the road.

Self-driving vehicle responds