That's... probably important.
In September of 2016, Waymo (still called Google back then) was granted a patent for a system that involved real-time detection of emergency vehicles. Now, Waymo's testing it out in the real world.
Waymo's new blog post discusses how the company set up shop with the Chandler, Arizona, police and fire departments to test how its self-driving Chrysler Pacifica minivans handle the ol' cherries and berries. It started by monitoring how those vehicles moved around the minivan, in order to give the vehicle an idea of what to expect and how to respond.
As the project currently stands, Waymo's minivans can now hear twice as far as they used to, the company says, and they use new software to help determine from which direction the sirens are approaching. That allows the car to decide whether to pull over or yield at an intersection.
Waymo is also training its software to recognize emergency vehicles even if they have a light pattern that hasn't been encountered in the past. Since different jurisdictions have different light patterns and colors -- in Chicago, police use blue lights, ambulances use red and fire trucks use green, for example -- it will need to act like a human does, determining whether those lights belong to an emergency vehicle or not.
Of course, Waymo didn't discuss every possible scenario. It didn't make mention of construction vehicles, which often use the same kind of light bars as emergency vehicles, except with amber lights. Nor did it discuss emergency vehicles that cruise with the lights on and the siren off. But it's pretty obvious that Waymo wants to make sure its self-driving cars don't accidentally make an emergency worse for someone else.