Google's autonomous cars drive millions of miles each day along virtual roads.
In its self-driving car report for January, Google notes that actual road testing is a vital but that simulation plays an equally important role.
Each time Google improves or refines a key feature in the technology, it tests the modification in a virtual environment using thousands of variations.
As a result, Google's vehicles drive a simulated 3 million miles each day.
"That's the equivalent of circling the equator five times every hour," the company said.
The report offers a glimpse of how Google is using simulation to replicate real-world driving.