Why Google’s Self-Driving Minivans Spent the Day With Fire Trucks

Courtesy of Waymo

Waymo, the Google self-driving project that spun out to become a business under Alphabet, is constantly putting its driverless vehicles through batteries of real-world tests to improve how they detect and respond to everyday—and not-so-common—scenarios.

This time, the company put its new self-driving minivans through an emergency vehicle testing day in Chandler, Ariz., to build a “library of sights and sounds” that will teach these driverless vehicles to respond safely to fire trucks, police motorcycles, ambulances, and even undercover law enforcement. Sensors on the minivans collected data at various speeds, distances, angles, and lighting conditions during the day of testing conducted with the Chandler Police and Fire Department.

Get Data Sheet, Fortune’s technology newsletter.

Waymo is testing all the time, and in various locations in the U.S. Head out to Chandler and it won’t take long before one of its Pacifica minivans passes through an intersection. The results of the test day are notable because Waymo shared some information about the new suite of sensors and an improved audio detection system performed on these minivans.

Waymo’s new audio detection system designed for its minivans can hear emergency vehicle sirens up to twice as far as with its previous suite of sensors, according to its blog post released Monday. Waymo also says its vehicles can see emergency vehicles and their flashing lights even further and clearer with its custom vision system, radars, and light detection and ranging radar known as LIDAR.

While that seems to denote progress, it’s hard to know exactly how significant the improvements are because the company doesn’t provide more details, like exactly how far can it hear and see now.