The autonomous car development company are working on making their cars responsive to police vehicles, ambulances and fire trucks.
Writing in a blog post, they explained: "Whether it's the high shrills of a fire truck or the flashing lights of a police cruiser, it's important for every driver to recognize the telltale signs of an emergency vehicle.
"Over the last few years, we've been teaching our self-driving cars to detect and respond to everything from fire trucks and ambulances to police cars and police motorcycles. Last month, we kicked off our latest efforts to improve the way we detect emergency vehicles.
"In collaboration with Chandler Police and Fire, we set up the first emergency vehicle testing day with our new self-driving minivans. Throughout the day and into the night, our vehicles - equipped with a powerful suite of sensors - observed police cars, motorcycles, ambulances, firetrucks, and even a few undercover vehicles as they trailed, passed and led our self-driving cars.
"As these emergency vehicles drove around, our sensors collected samples at various speeds, distances, and angles - all with the goal of building up a library of sights and sounds to help teach our self-driving cars to respond safely to emergency vehicles on the road."
The new information collected means the vans can detect where the siren is most likely to be coming from and allows the vehicle to stop or go, whatever is safest.
They added: "Today, our self-driving minivans are capable of hearing twice as far as they could with our last suite of sensors. And with our new sensors, we're teaching our software to discern which direction the sirens are likely coming from.
"Drivers often hear the sirens of an emergency vehicle first, so being able to gauge the direction of an oncoming fire truck or ambulance allows our self-driving vehicles to make smarter and safer decisions. For example, our vehicles may pull over if an emergency vehicle is coming from behind, but yield at an intersection if our sensors detect sirens coming up ahead."