Late last week, Waymo issued a report on its self-driving cars. Given the length of time that the company has been testing autonomous vehicles (eight years) on public roads (3.5 million miles) and in labs (2.5 million simulated miles in 2016 alone), there’s a lot of info to sift through.

As you might imagine, some of that info involves collisions–not just how autonomous vehicles avoid them, but also how law enforcement agencies are being trained to assess crashes involving self-driving cars. Re-Code reports:

By working with the police department in Chandler, AZ, for example, Waymo has been able to train its cars to yield, pull over, or stop when it hears or sees sirens. This is obviously helpful in situations when these emergency vehicles are trying to quickly get to the scene of a crash. The car will hear the sirens and move out of the way.

But it’s also important for when Waymo’s self-driving cars themselves get into an accident. Using audio data, the cars are able to detect what direction the emergency vehicles are coming from. This helps the cars respond efficiently and safely.

“Our sensors collected samples at various speeds, distances, and angles—building up a library of sights and sounds that will help our vehicles respond safely to emergency vehicles on the road,” the report reads.