Inside Waymo's self-driving effort, including its physical test base, called Castle, and Carcraft VR simulations, where 25K virtual cars drive 8M miles per day
In a corner of Alphabet's campus, there is a team working on a piece of software that may be the key to self-driving cars.
Context & Ripple Effects
This 2017 profile is the earliest look at the two-track validation system Waymo still runs today: the Castle proving ground on Alphabet's campus, where hardware and edge cases get tested physically, and Carcraft, the VR simulator where 25,000 virtual cars drive about 8 million miles a day. The pairing matters because it shows Waymo treating simulation not as a supplement to road testing but as the primary engine of driver development.
The arc since then confirms the bet: Waymo applied to run cars without safety drivers in California in 2018, opened its Phoenix depot and free Early Rider program that same year, and by 2021 had graduated from Carcraft to Simulation City, a full virtual world for training and validating the Waymo Driver before it ever touches pavement.
First-order effects
- Waymo can iterate on its self-driving software at a rate physical fleets cannot match — rare or dangerous scenarios get rehearsed millions of times virtually before any Chrysler van encounters them at Castle or on public roads.
- Alphabet gets a defensible data asset: every simulated mile feeds back into the same models Google Brain researchers work on, compounding Waymo's lead over rivals with smaller test fleets.
Second-order effects
- Competitors are pushed toward the same simulation-heavy playbook, because matching Waymo's real-world mileage alone would take years and enormous fleet cost — the moat shifts from cars driven to scenarios covered.
- Regulators evaluating applications like Waymo's California driverless-testing request gain a new evidentiary category: billions of validated simulated miles become part of the safety case companies present.
Third-order effects
- If the pattern holds, autonomy becomes a compute-and-simulation business first and a vehicle business second — the winners are whoever owns the largest validated scenario libraries, which favors Alphabet-scale infrastructure owners.
- That structure also concentrates the field: startups without Alphabet's campus-scale test bases and simulation budgets must either license someone else's stack or exit, pushing consolidation toward a few full-stack operators.
The trend: Self-driving development is shifting from real-road mileage races to simulation-first validation, where virtual miles and physical proving grounds like Castle together determine who can safely deploy.