Waymo parked its fleet of prototype self-driving cars in response to the coronavirus pandemic, but that doesn’t mean the company has stopped working on autonomous driving tech. Even with employees working from home, Waymo is still capable of running simulations 24 hours a day, seven days a week, continuing to develop autonomous driving systems, a company press release said.

Simulations were a big part of Waymo’s operations before the pandemic. One day in simulation is equivalent to 100 years of real-world driving, according to Waymo. The majority of development work on any new piece of software is already done in simulation, before being released for use in actual cars, the company noted.

Real-world testing is important, but it can also be limiting, according to Waymo. Simulation gives engineers control over what scenarios the system encounters, allowing them to focus on the most difficult or unusual scenarios. Known in the industry as “corner cases,” these are scenarios that occur rarely in the real world but need to be planned for nonetheless.

In a simulation, engineers can replay specific moments from 20 million miles of real-world driving by Waymo’s test vehicles, according to the company, using data from cars’ onboard sensors. Engineers can also tweak these scenarios, increasing the speed of oncoming traffic or adding a cyclist just to see how the system reacts, or create entirely artificial scenarios, according to Waymo. This lets engineers zero in on specific areas that need to be tested.

Waymo can even simulate passengers. The company has used feedback from real people to create machine learning models, which attempt to predict how driving behavior impacts passenger comfort. Fine-tuning the way autonomous cars for smooth driving helps ensure that no one gets car sick.

Running these kinds of simulations normally requires a lot of computing power, Waymo noted, but the company said it has found workarounds. Web versions of the most commonly used applications allow engineers to use their home computers, the company said.

Prior to the coronavirus shutdown, Waymo operated a ridesharing service, delivered packages for UPS, and operated a small fleet of prototype autonomous trucks. The current fleet of passenger-carrying vehicles includes Chrysler Pacifica Hybrid minivans and Jaguar I-Pace electric cars.