Today,  most advanced autonomous vehicles are ones that can drive themselves on the highway, park themselves and change lanes . But these cars still have a way to go before they can handle every situation imaginable. To improve its fleet, Waymo is teaching its self-driving Chrysler Pacifica minivans to detect fire trucks, ambulances, police cars and motorcycles, and even undercover vehicles.

Waymo put its updated fleet of autonomous cars through an emergency vehicle test day in Arizona

Recently, Waymo put its updated fleet of autonomous cars through an emergency vehicle test day in Arizona. During the tests, autonomous car sensors recorded encounters with emergency vehicles at different speeds and distances, creating lots of data that will help teach self-driving cars to better respond to these situations.

With its latest sensor technology, Waymo’s autonomous vehicles can hear twice as far as they could with the older sensors. The software can also discern which direction the sirens are likely coming from, helping the self-driving vehicle to get out of the way. Meanwhile, other sensors help the vehicles see flashing lights.

Currently, Waymo is giving residents of Phoenix, Arizona the opportunity to ride in one of its self-driving vehicles. As part of this “early rider” program, hundreds of people will use Waymo’s self-driving cars on a daily basis, and in exchange for the free service, they will provide feedback on the experience.

As of last month, Waymo had 600 Pacifica plug-in hybrids in its fleet. The models are equipped with Waymo’s sensors, radar, and LiDAR necessary for autonomous driving.