How Cruise vehicles return to the garage autonomously in heavy rain

Cruise doesn’t carry passengers in heavy rain. The operational design domain (ODD) in their CPUC permit (PDF) only allows services in light rain.

I’ve always wondered how they implement this operationally. For example, Waymo preemptively launches all cars with operators in the driver’s seat anytime there’s rain in the forecast. Cruise has no such policy: I have never seen them assign operators to customer-facing vehicles.

Yet Cruise claims to run up to 100 driverless vehicles concurrently. It would be impractical to dispatch a human driver to each vehicle whenever it starts raining. When the latest atmostpheric river hit San Francisco, I knew it was my chance to find out how it worked.

Monitoring the Cruise app

As the rain intensified, as expected, all cars disappeared from Cruise’s app and the weather pause icon appeared.

But then something unusual happened. The app returned to its normal state. A few cars showed up near a hole in the geofence — and they were actually hailable.

Visiting the garage

I drove over to find that this street is the entrance to one of Cruise’s garages. The same location has been featured in Cruise executives’ past tweets promoting the service.¹

Despite the heavy rain and gusts strong enough to blow my hat/jacket off, a steady stream of Cruise vehicles were returning themselves to the garage in driverless mode.

In total, I observed:

• 8 driverless vehicles
• 1 manually driven vehicle
• 1 support vehicle (unmodified Chevy Bolt not capable of autonomous driving)

Two vehicles skip the garage

After the first six driverless vehicles returned, the next two kept driving past the garage. I followed them in my own car. They drove for about 16 minutes, handling large puddles and road spray without noticeable comfort issues. Eventually they looped back to the garage and successfully entered.

I’m not totally sure what happened here. I can think of two reasonable explanations:

1. Boring: The cars missed the turn for some unknown reason.
2. Exciting: Cruise has implemented logic to avoid overwhelming the operations team’s ability to put cars back in the garage. If there are too many vehicles waiting to return, subsequent cars take a detour to kill time instead of blocking the driveway.

Key take-aways

• Cruise is capable of handling heavy rain in driverless mode.
• The majority of Cruise vehicles returned to the garage autonomously. This enables them to handle correlated events, such as rain, without deploying a large operations team.
• Cruise may have implemented “take a lap around the block” logic to avoid congestion at the garage entrance.

---